U.S. patent application number 15/787790 was filed with the patent office on 2019-04-25 for latency correction between transport layer host and deterministic interface circuit.
The applicant listed for this patent is Cisco Technology, Inc.. Invention is credited to ERIC MICHEL LEVY-ABEGNOLI, PASCAL THUBERT, PATRICK WETTERWALD.
Application Number | 20190124006 15/787790 |
Document ID | / |
Family ID | 66171291 |
Filed Date | 2019-04-25 |
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United States Patent
Application |
20190124006 |
Kind Code |
A1 |
THUBERT; PASCAL ; et
al. |
April 25, 2019 |
LATENCY CORRECTION BETWEEN TRANSPORT LAYER HOST AND DETERMINISTIC
INTERFACE CIRCUIT
Abstract
In one embodiment, a method comprises establishing, by a
deterministic device interface circuit, a deterministic link with a
peer deterministic interface circuit within a deterministic data
network based on identifying a repeating deterministic schedule for
transmitting each data packet, allocated to the deterministic
schedule, at a corresponding transmission instance coinciding with
a reception instance by the peer deterministic interface circuit;
determining a latency between sending a request for data to a host
device via a non-deterministic data link provided by a network
switch, and receiving from the host device a transport layer packet
responsive to the request; and sending an instruction to the host
device for initiating transfer of the transport layer packet, the
instruction correcting for the latency and enabling the
deterministic device interface circuit to receive the transport
layer packet for transmission of a corresponding data packet on the
deterministic link at the corresponding transmission instance.
Inventors: |
THUBERT; PASCAL; (La Colle
Sur Loup, FR) ; LEVY-ABEGNOLI; ERIC MICHEL;
(Valbonne, FR) ; WETTERWALD; PATRICK; (Mouans
Sartoux, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cisco Technology, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
66171291 |
Appl. No.: |
15/787790 |
Filed: |
October 19, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 47/193 20130101;
H04L 47/2416 20130101; H04L 47/39 20130101; H04L 47/12
20130101 |
International
Class: |
H04L 12/801 20060101
H04L012/801; H04L 12/853 20060101 H04L012/853 |
Claims
1. A method comprising: establishing, by a deterministic device
interface circuit, a deterministic link with a peer deterministic
interface circuit within a deterministic data network based on
identifying a repeating deterministic schedule for transmitting
each data packet, allocated to the deterministic schedule, at a
corresponding transmission instance coinciding with a reception
instance by the peer deterministic interface circuit; determining a
latency between sending a request for data to a host device via a
non-deterministic data link provided by a network switch, and
receiving from the host device a transport layer packet responsive
to the request; and sending an instruction to the host device for
initiating transfer of the transport layer packet, the instruction
correcting for the latency and enabling the deterministic device
interface circuit to receive the transport layer packet for
transmission of a corresponding data packet on the deterministic
link at the corresponding transmission instance.
2. The method of claim 1, wherein: the determining includes
determining the latency exceeds a prescribed time interval between
each transmission instance in the deterministic schedule; and the
sending of the instruction includes setting a transfer window to an
initial transfer window equal to a first integer multiple of the
prescribed time interval and exceeding the latency, first
transmitting at a request instance, from the deterministic device
interface circuit to the host device, a first request for a first
transport layer packet, the request instance preceding the
corresponding transmission instance for the first transport layer
packet by the transfer window, and transmitting each remaining of
the integer multiple of the requests following the first request at
the corresponding request instance after each prescribed time
interval.
3. The method of claim 2, wherein: the determining of the latency
further includes setting a guard window that encompasses a jitter
variation on the non-deterministic data link; determining whether
one of the transport layer packets is received at an excess latency
that exceeds the corresponding request instance by more than the
initial transfer window and the guard window; and increasing the
transfer window by at least the prescribed interval in response to
detecting the one transport layer received after the excess
latency.
4. The method of claim 3, further comprising the deterministic
network interface circuit sending to the host device an exceptional
request message, for a next transport layer packet, before the next
request message scheduled for transmission after the prescribed
time interval.
5. The method of claim 2, wherein the sending of the instruction
includes at least one of adjusting the transfer window or
transmitting an exceptional request message to the host device,
based on reception of the transport layer packets responsive to the
request, for maintaining storage of a single transport layer packet
in a transmit buffer of the deterministic network interface circuit
after each transmission instance of a corresponding transmitted
data packet from the transmit buffer.
6. The method of claim 2, wherein the determining includes:
receiving, from the host device for each integer multiple of the
requests, a number of packets sent for the corresponding integer
multiple of requests; and determining, by the deterministic network
interface circuit for each integer multiple of the requests,
whether a corresponding one of the requests was not received by the
host device based on the corresponding number of packets sent
relative to a corresponding count of successful packet
transmissions and a corresponding count of missed transmit
opportunities on the deterministic link; the instruction specifying
that the host device discards a discards a discard-eligible
transport layer packet and transfers a subsequent transport layer
packet, at the corresponding request instance, in place of the
discard-eligible transport layer packet.
7. The method of claim 1, further comprising the deterministic
device interface circuit sending a second instruction to the host
device for transferring transport layer packets at a transfer rate
based on the deterministic schedule establishing a transmission
rate as a prescribed time interval between each transmission
instance; the determining of the latency includes the deterministic
device interface circuit identifying a rate difference between a
rate of receiving the transport layer packets from the host device
and the transmission rate of the deterministic schedule; the
sending including the deterministic device interface circuit
specifying in the instruction one of an exceptional request message
or a suppress message for compensation of the rate difference, the
exceptional request message for a next transport layer packet
before a next scheduled transport layer packet according to the
transfer rate, the suppress message for suppressing transmission of
the next scheduled transport layer packet that is scheduled
according to the transfer rate.
8. The method of claim 7, wherein the sending further includes the
deterministic device interface circuit sending at least one of a
timing advance message or a timing delay message for further
compensation of the rate difference, the timing advance message
causing the host device to advance its timing for the next
scheduled transport layer packet that is scheduled according to the
transfer rate, the timing delay message causing the host device to
delay its timing for the next scheduled transport layer packet that
is scheduled according to the transfer rate.
9. An apparatus comprising: a memory circuit configured for storing
a data packet within a transmit buffer; and a deterministic
processing circuit configured for establishing a deterministic link
with a peer deterministic interface circuit within a deterministic
data network based on identifying a repeating deterministic
schedule for transmitting each data packet, allocated to the
deterministic schedule, at a corresponding transmission instance
coinciding with a reception instance by the peer deterministic
interface circuit; the deterministic processing circuit configured
for determining a latency between sending a request for data to a
host device via a non-deterministic data link provided by a network
switch, and receiving from the host device a transport layer packet
responsive to the request; the deterministic processing circuit
configured for sending an instruction to the host device for
initiating transfer of the transport layer packet, the instruction
correcting for the latency and enabling the apparatus to receive
the transport layer packet for transmission of a corresponding data
packet on the deterministic link at the corresponding transmission
instance.
10. The apparatus of claim 9, wherein: the deterministic processing
circuit is configured for determining the latency exceeds a
prescribed time interval between each transmission instance in the
deterministic schedule; and the deterministic processing circuit is
configured for setting a transfer window to an initial transfer
window equal to a first integer multiple of the prescribed time
interval and exceeding the latency; the deterministic processing
circuit further configured for first transmitting at a request
instance to the host device a first request for a first transport
layer packet, the request instance preceding the corresponding
transmission instance for the first transport layer packet by the
transfer window, the deterministic processing circuit further
configured for transmitting each remaining of the integer multiple
of the requests following the first request at the corresponding
request instance after each prescribed time interval.
11. The apparatus of claim 10, wherein the deterministic processing
circuit is configured for: setting a guard window that encompasses
a jitter variation on the non-deterministic data link; determining
whether one of the transport layer packets is received at an excess
latency that exceeds the corresponding request instance by more
than the initial transfer window and the guard window; and
increasing the transfer window by at least the prescribed interval
in response to detecting the one transport layer received after the
excess latency.
12. The apparatus of claim 11, wherein the deterministic processing
circuit is configured for sending to the host device an exceptional
request message, for a next transport layer packet, before the next
request message scheduled for transmission after the prescribed
time interval.
13. The apparatus of claim 10, wherein the deterministic processing
circuit is configured for at least one of adjusting the transfer
window or transmitting an exceptional request message to the host
device, based on reception of the transport layer packets
responsive to the request, for maintaining storage of a single
transport layer packet in the transmit buffer after each
transmission instance of a corresponding transmitted data packet
from the transmit buffer.
14. The apparatus of claim 10, wherein the deterministic processing
circuit is configured for: receiving, from the host device for each
integer multiple of the requests, a number of packets sent for the
corresponding integer multiple of requests; determining, for each
integer multiple of the requests, whether a corresponding one of
the requests was not received by the host device based on the
corresponding number of packets sent relative to a corresponding
count of successful packet transmissions and a corresponding count
of missed transmit opportunities on the deterministic link; and
specifying in the instruction that the host device discards a
discard-eligible transport layer packet and transfers a subsequent
transport layer packet, at the corresponding request instance, in
place of the discard-eligible transport layer packet.
15. The apparatus of claim 9, wherein the deterministic processing
circuit is configured for: sending a second instruction to the host
device for transferring transport layer packets at a transfer rate
based on the deterministic schedule establishing a transmission
rate as a prescribed time interval between each transmission
instance; identifying a rate difference between a rate of receiving
the transport layer packets from the host device and the
transmission rate of the deterministic schedule; specifying in the
instruction one of an exceptional request message or a suppress
message for compensation of the rate difference, the exceptional
request message for a next transport layer packet before a next
scheduled transport layer packet according to the transfer rate,
the suppress message for suppressing transmission of the next
scheduled transport layer packet that is scheduled according to the
transfer rate.
16. The apparatus of claim 15, wherein the deterministic processing
circuit is configured for sending at least one of a timing advance
message or a timing delay message for further compensation of the
rate difference, the timing advance message causing the host device
to advance its timing for the next scheduled transport layer packet
that is scheduled according to the transfer rate, the timing delay
message causing the host device to delay its timing for the next
scheduled transport layer packet that is scheduled according to the
transfer rate.
17. One or more non-transitory tangible media encoded with logic
for execution by a machine and when executed by the machine
operable for: establishing, by the machine implemented as a
deterministic device interface circuit, a deterministic link with a
peer deterministic interface circuit within a deterministic data
network based on identifying a repeating deterministic schedule for
transmitting each data packet, allocated to the deterministic
schedule, at a corresponding transmission instance coinciding with
a reception instance by the peer deterministic interface circuit;
determining a latency between sending a request for data to a host
device via a non-deterministic data link provided by a network
switch, and receiving from the host device a transport layer packet
responsive to the request; and sending an instruction to the host
device for initiating transfer of the transport layer packet, the
instruction correcting for the latency and enabling the
deterministic device interface circuit to receive the transport
layer packet for transmission of a corresponding data packet on the
deterministic link at the corresponding transmission instance.
18. The one or more non-transitory tangible media of claim 17,
wherein: the determining includes determining the latency exceeds a
prescribed time interval between each transmission instance in the
deterministic schedule; and the sending of the instruction includes
setting a transfer window to an initial transfer window equal to a
first integer multiple of the prescribed time interval and
exceeding the latency, first transmitting at a request instance,
from the deterministic device interface circuit to the host device,
a first request for a first transport layer packet, the request
instance preceding the corresponding transmission instance for the
first transport layer packet by the transfer window, and
transmitting each remaining of the integer multiple of the requests
following the first request at the corresponding request instance
after each prescribed time interval.
19. The one or more non-transitory tangible media of claim 17,
further operable for sending a second instruction to the host
device for transferring transport layer packets at a transfer rate
based on the deterministic schedule establishing a transmission
rate as a prescribed time interval between each transmission
instance; the determining of the latency includes identifying a
rate difference between a rate of receiving the transport layer
packets from the host device and the transmission rate of the
deterministic schedule; the sending including specifying in the
instruction one of an exceptional request message or a suppress
message for compensation of the rate difference, the exceptional
request message for a next transport layer packet before a next
scheduled transport layer packet according to the transfer rate,
the suppress message for suppressing transmission of the next
scheduled transport layer packet that is scheduled according to the
transfer rate.
20. The one or more non-transitory tangible media of claim 19,
wherein the sending further includes sending at least one of a
timing advance message or a timing delay message for further
compensation of the rate difference, the timing advance message
causing the host device to advance its timing for the next
scheduled transport layer packet that is scheduled according to the
transfer rate, the timing delay message causing the host device to
delay its timing for the next scheduled transport layer packet that
is scheduled according to the transfer rate.
Description
TECHNICAL FIELD
[0001] The present disclosure generally relates to a latency
correction between a transport layer host and a deterministic
interface circuit.
BACKGROUND
[0002] This section describes approaches that could be employed,
but are not necessarily approaches that have been previously
conceived or employed. Hence, unless explicitly specified
otherwise, any approaches described in this section are not prior
art to the claims in this application, and any approaches described
in this section are not admitted to be prior art by inclusion in
this section.
[0003] The Internet Engineering Task Force (IETF) Deterministic
Networking (DetNet) Working Group is addressing proposals for
satisfying the stringent requirements of deterministic data
networks (e.g., minimal jitter (i.e., minimal packet delay
variation), low latency, minimal packet loss, and high
reliability). The DetNet Working Group is investigating proposals
for networks that are under a single administrative control or
within a closed group of administrative control, where such
networks within the single/closed group of administrative control
can provide forwarding along a multi-hop path with the
deterministic properties of controlled latency, low packet low, low
packet delay variation, and high reliability. One proposal for low
power and lossy network (LLN) devices is a routing protocol that
provides IPv6 routing using time slotted channel hopping (TSCH)
based on IEEE 802.15.4e ("6TiSCH"), enabling wireless LLN devices
to use low-power operation and channel hopping for higher
reliability.
[0004] Deterministic transmission in wired networks can use time
sensitive networking (TSN) and/or audio/video bridging (AVB) for
deterministic networks such as professional and home audio/video,
multimedia in transportation, vehicle engine control systems,
and/or otter general industrial and/or vehicular applications.
Neither TSN nor AVB use time slots; rather, TSN uses time-based
shapers that allocate time slices and guard bands to cause a data
packet to be sent or received at a given intermediate node (i.e.,
hop) along a path at a prescribed precise time that is reserved
exclusively for the given hop; AVB can use credit-based shapers
that ensure bounded latency transmit/receive queues in each hop
without congestion, thereby ensuring a bounded latency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Reference is made to the attached drawings, wherein elements
having the same reference numeral designations represent like
elements throughout and wherein:
[0006] FIGS. 1A-1J illustrates one or more host devices comprising
a transport layer providing deterministic transport of transport
layer packets across multiple deterministic links in an example
deterministic data network, according to an example embodiment.
[0007] FIG. 2 illustrates a second example deterministic data
network having an intermediate host device comprising a transport
layer providing deterministic transport of transport layer packets
between deterministic links of different distinct deterministic
domains, according to an example embodiment.
[0008] FIG. 3 illustrates an example implementation of any one of
the devices of FIGS. 1 and/or 2, according to an example
embodiment.
[0009] FIGS. 4A-4C illustrate an example method of a transport
layer providing deterministic transport of transport layer packets
across multiple deterministic links, according to an example
embodiment.
[0010] FIG. 5 illustrates an example pre-fetch interval, determined
by the transport layer of FIGS. 1 and/or 2, for deterministic
retrieval of each transport layer packet by a deterministic network
interface circuit, according to an example embodiment.
[0011] FIGS. 6A and 6B illustrate an example method of identifying
a failure case in a missed transmission opportunity, and mitigating
against the failure to ensure deterministic transport across the
multiple deterministic data links, according to an example
embodiment.
[0012] FIG. 7 illustrates an example diagram of the transport layer
in a host device and a deterministic network interface circuit
executing mitigation against a missed transmission opportunity,
according to an example embodiment.
[0013] FIG. 8 illustrates another example of deterministic
interface circuits providing deterministic transport of transport
layer packets across multiple deterministic links, based on
correcting latency in retrieving transport layer packets from a
host device via a non-deterministic switch, according to an example
embodiment.
[0014] FIGS. 9A and 9B illustrate a deterministic interface circuit
correcting latency in retrieving transport layer packets from a
host device for deterministic transport on a deterministic link,
according to an example embodiment.
[0015] FIG. 10 illustrates an example transfer window that corrects
for latency by requesting a transport layer packet at a request
instance preceding a corresponding transmission instance by at
least a transfer window, while minimizing latency in the
deterministic network interface circuit, according to an example
embodiment.
DESCRIPTION OF EXAMPLE EMBODIMENTS OVERVIEW
[0016] In one embodiment, a method comprises: establishing, by a
deterministic device interface circuit, a deterministic link with a
peer deterministic interface circuit within a deterministic data
network based on identifying a repeating deterministic schedule for
transmitting each data packet, allocated to the deterministic
schedule, at a corresponding transmission instance coinciding with
a reception instance by the peer deterministic interface circuit;
determining a latency between sending a request for data to a host
device via a non-deterministic data link provided by a network
switch, and receiving from the host device a transport layer packet
responsive to the request; and sending an instruction to the host
device for initiating transfer of the transport layer packet, the
instruction correcting for the latency and enabling the
deterministic device interface circuit to receive the transport
layer packet for transmission of a corresponding data packet on the
deterministic link at the corresponding transmission instance.
[0017] In another embodiment, an apparatus comprises a memory
circuit, and a deterministic processing circuit. The memory circuit
configured for storing a data packet within a transmit buffer. The
deterministic processing circuit is configured for establishing a
deterministic link with a peer deterministic interface circuit
within a deterministic data network based on identifying a
repeating deterministic schedule for transmitting each data packet,
allocated to the deterministic schedule, at a corresponding
transmission instance coinciding with a reception instance by the
peer deterministic interface circuit. The deterministic processing
circuit further is configured for determining a latency between
sending a request for data to a host device via a non-deterministic
data link provided by a network switch, and receiving from the host
device a transport layer packet responsive to the request. The
deterministic processing circuit further is configured for sending
an instruction to the host device for initiating transfer of the
transport layer packet, the instruction correcting for the latency
and enabling the apparatus to receive the transport layer packet
for transmission of a corresponding data packet on the
deterministic link at the corresponding transmission instance.
[0018] In another embodiment, one or more non-transitory tangible
media are encoded with logic for execution by a machine and when
executed by the machine operable for: establishing, by the machine
implemented as a deterministic device interface circuit, a
deterministic link with a peer deterministic interface circuit
within a deterministic data network based on identifying a
repeating deterministic schedule for transmitting each data packet,
allocated to the deterministic schedule, at a corresponding
transmission instance coinciding with a reception instance by the
peer deterministic interface circuit; determining a latency between
sending a request for data to a host device via a non-deterministic
data link provided by a network switch, and receiving from the host
device a transport layer packet responsive to the request; and
sending an instruction to the host device for initiating transfer
of the transport layer packet, the instruction correcting for the
latency and enabling the deterministic device interface circuit to
receive the transport layer packet for transmission of a
corresponding data packet on the deterministic link at the
corresponding transmission instance.
DETAILED DESCRIPTION
[0019] Particular embodiments enable deterministic transport of a
flow of application data across multiple deterministic data links
(i.e., deterministic links) in a deterministic data network, even
if the executable application generating the application data
(i.e., the host device) is incapable of providing the flow of
application data according to the precise synchronization
requirements of the deterministic links, based on a transport layer
storing the application data in a transport buffer circuit as
transport layer packets, and multiple deterministic network
interface circuits deterministically retrieving the transmit layer
packets, from the transport buffer circuit in the host device for
deterministic transmission across the respective deterministic
links.
[0020] Each deterministic network interface circuit can
deterministically obtain a transmit layer packet from the host
device, even if the data connection between the deterministic
network interface circuit and the host device is via a
non-deterministic data link provided by a network switch (e.g., an
unmanaged Ethernet switch), based on correcting for detected
latency. The deterministic network interface circuit is configured
for determining a latency between sending a request for data to the
host device via the non-deterministic data link (via the network
switch), and receiving from the host device a transport layer
responsive to the request. In response to determining the latency,
the deterministic network interface circuit is configured for
sending an instruction to the host device for initiating transfer
of the transport layer packet, where the instruction corrects for
the detected latency. The instruction to the host device enables
the deterministic device interface circuit to receive the transport
layer packet for transmission of a corresponding data packet on the
deterministic link at the corresponding transmission instance.
[0021] Hence, example embodiments enable deterministic transport of
data between a host device and one or more deterministic network
interface circuits, for transport via a deterministic network, even
if the data link between the host device and the deterministic
network interface circuits suffers from latency, jitter, drift,
etc., that otherwise would prevent a deterministic transport of
data from the host device to the deterministic network interface
circuits.
[0022] A description will first be provided of the host device
providing deterministic transport of a flow of application data via
transport layer packets across multiple deterministic links in a
deterministic data network, followed by a description of the
transport layer identifying a failure cause and providing
mitigation against any increase in latency based on selectively
executing a corrective action in response to the identified failure
cause. A description will then be provided of executing latency
correction between a transport layer host and a deterministic
interface circuit.
TRANSPORT LAYER PROVIDING DETERMINISTIC TRANSPORT ACROSS MULTIPLE
DETERMINISTIC DATA LINKS
[0023] Particular embodiments enable deterministic transport of a
flow of application data across multiple deterministic data links
(i.e., deterministic links) in a deterministic data network, even
if the executable application generating the application data is
incapable of providing the flow of application data according to
the precise synchronization requirements of the deterministic
links, based on a transport layer storing the application data in a
transport buffer circuit as transport layer packets having
respective transport sequence identifiers that identify their
relative positions relative to a transmit order, and causing
deterministic network interface circuits to deterministically
retrieve the transmit layer packets, in the transmit order, from
the transport buffer circuit for deterministic transmission across
the respective deterministic links. The transport sequence
identifiers enable a destination transport layer to recover the
transmit order of the transport layer following the deterministic
transmission across the deterministic links, regardless of order of
reception thereof by the destination transport layer.
[0024] A deterministic data network typically requires strict
timing synchronization and scheduling along each hop from a source
host to a destination host. A network manager (e.g., a TSN
controller, scheduler, etc.) within the deterministic data network
can have a prescribed management domain (i.e., deterministic
domain) for controlling each network device along the deterministic
path, starting with the source deterministic network interface
circuits transmitting the data packets into the deterministic data
network, continuing with each deterministic switching device along
the deterministic path, and ending with the destination
deterministic network interface circuits at the end of the
deterministic path. Hence, the network controller can establish,
for each deterministic data link along a deterministic path, a
scheduled transmit time for the corresponding transmitting
deterministic network interface circuit, a scheduled receive time
for the corresponding receiving deterministic network interface
circuit, and a common time reference used for synchronization of
each of the deterministic network devices in the deterministic
domain. Deterministic networks can be used for industrial
automation, vehicle control systems, and other systems that require
precise delivery of control commands to a controlled device.
However, implementing deterministic networking can include
stringent deterministic constraints such as packet delivery within
a prescribed latency, zero or near-zero jitter, high packet
delivery ratios, etc.
[0025] The example embodiments ensure that even if transport layer
packets are received at a destination host in a receive order that
differs from the transmit order (for example due to the different
deterministic links having different relative schedules and/or
different latencies), the transport layer executed in the
destination host can reorder the received transport layer packets
from the received order into the transmit order based on the
respective transport sequence identifiers within the received
transport layer packets. The example embodiments also can be
executed in an intermediate host device that can reorder the
received transport layer packets from the received order into the
transmit order, prior to retransmission on different deterministic
links, for example if the intermediate host device receives the
transport layer packets from first deterministic links in a first
deterministic domain and causes retransmission in the transport
order via second deterministic links in a second different
deterministic domain (e.g., using different number of deterministic
data links, different schedules, different management entity,
etc.).
[0026] Existing transport mechanisms (e.g., Transmission Control
Protocol, or "TCP") are incapable of providing deterministic
transmission of a flow of data packets across multiple
deterministic links because such transport mechanisms have
constraints that are inconsistent with the requirements of a
deterministic network. For example, deterministic networking (e.g.,
DetNet, TSN) relies on a fixed bandwidth or throughput for reliable
delivery of data packets at a precise reception time; in contrast,
TCP is configured for adapting to bandwidth variations in
non-deterministic data networks by attempting to aggressively claim
more bandwidth for data transmission until reaching a point where
packet loss occurs, in response to which TCP will "throttle back"
its use of bandwidth (e.g., the bandwidth utilization of TCP
resembles a sawtooth wave) and retry transmission of the lost data
packet after a timeout window. Hence, the variable bandwidth
utilization of TCP conflicts with the fixed bandwidth of
deterministic networking.
[0027] TCP also conflicts with the requirements of a deterministic
network device receiving a data packet at a precisely-scheduled
receive time, because TCP is configured for retransmitting a lost
packet during a retry attempt after a timeout window; hence, any
TCP-based retry attempt would be improper in deterministic
networking because the retry attempt after the timeout window would
be too late, i.e., substantially after the precisely-scheduled
receive time.
[0028] Further, deterministic networking can establish stringent
deterministic constraints based on defining a transmission schedule
relative to: (1) a period of time "T"; (2) a maximum packet size
"F"; and a maximum number of data packets "N" that can be
transmitted on a deterministic link within the period of time "T".
Hence, a deterministic network interface circuit can transmit on a
deterministic link, at a scheduled transmission time within the
period of time "T", a maximum number of "N" data packets having a
maximum size "F"; in other words, a data packet exceeding size "F"
is dropped (by the receiving deterministic network interface
circuit) if transmitted on the deterministic link; further, if
"N+1" packets are transmitted on the deterministic data link at the
scheduled transmission time within the period of time "T", the
first "N" packets would be accepted (by the receiving deterministic
network interface circuit) and the "N+1" packet would be dropped.
TCP does not provide for transmitting, at a scheduled transmission
time within the period of time "T", a maximum number of "N" data
packets having a maximum size "F".
[0029] Hence, example embodiments enable an executable application
that generates a flow of application data to utilize multiple
deterministic links (as opposed to relying on a single
deterministic link such as a TSN link or AVB link, etc.), without
the necessity of the executable application coordinating with a
network manager that provides time-aware scheduling of the
deterministic data links for enforcement of precise synchronization
requirements according to prescribed Quality of Service (QoS)
Service Level Agreements (SLA) within the deterministic network. As
described below, the transport layer can determine a preferred (or
optimized) size available on a deterministic link 18 (e.g., 75
kbps), and proactively request additional deterministic links 18
for deterministic transport of the transport layer packets
according to the QoS requirements (e.g., 100 kbps) required by the
flow of application data.
[0030] FIGS. 1A-1J illustrate one or more host devices 10, 10',
each comprising a processor circuit 12 configured for executing a
transport layer 14 for providing deterministic transport of
transport layer packets 16 across multiple deterministic links 18
in an example deterministic data network 20, according to an
example embodiment. The deterministic data network 20 of FIGS.
1A-1J is illustrated for simplicity as comprising two or more
peer-to-peer TSN data links "TSN Link 1" 18 and "TSN Link 2"
between deterministic network interface circuits 22, illustrated as
a TSN "Line card 1" 22a, TSN "Line card 2" 22b, TSN "Line card 1"
22c, and TSN "Line card 1" 22d. The deterministic data network 20
also can include a network manager device 24 configured for
controlling establishment of the deterministic links 18, by the
deterministic network interface circuits 22, according to
prescribed deterministic constraints established and maintained by
the network manager device 24. In particular, the network manager
device 24 can send instructions to each of the deterministic
network interface circuits 22 for establishment of a deterministic
link 18 with a peer deterministic network interface circuit (i.e.,
peer deterministic interface circuits) 22 according to the
above-described deterministic constraints, including for example a
transmission time "t_TSN" according to a repeating schedule, a
prescribed transmission period of time "T", and a maximum number of
"N" data packets having a maximum size "F" that can be transmitted
during the transmission time period "T". The network manager device
24 can cause the deterministic network interface circuits 22 to
establish the deterministic links 18, for example as TSN links
according to IEEE 802.1Qbv. The maximum size "F" can be established
by the Service Level Agreement (SLA), in terms of the maximum
packet size "F", and the maximum number of "N" data packets per
unit time "T"; alternately, the SLA can specify a minimum delay
between packets.
[0031] The deterministic data network 20 also can be implemented as
shown FIG. 2, which illustrates a second example deterministic data
network 20'. The deterministic data network 20' can include a
plurality of deterministic network interface circuits 22 (22e
through 22m) implemented within one or more switching devices 38,
implemented for example as a commercially-available Cisco.RTM.
Industrial Ethernet (IE) 4000 Series and/or IE 5000 Series Switch
from Cisco Systems, San Jose, Calif. The deterministic data network
20' also includes a first network manager device 24a configured for
establishing the deterministic links 18 within a first
deterministic domain 26a based on deterministic constraints
established by the network manager device 24a and sent to each of
the deterministic network interface circuits 22 (e.g., 22e through
22j) establishing the deterministic links 18 in the deterministic
domain 26a. As illustrated in FIG. 2, the source host device 10 can
be coupled to the deterministic network interface circuits 22e and
22f via a Top-of-Rack (TOR) Switch 28, implemented for example as a
commercially-available Cisco.RTM. Catalyst 4900 Series Switch from
Cisco Systems, San Jose, Calif. Hence, the source host device 10,
the TOR switching device 28, and the deterministic network
interface circuits 22e and 22f can be implemented within a single
rack mount, for example within a data center or within an
industrial network.
[0032] The deterministic data network 20' also can include a second
network manager device 24b configured for establishing the
deterministic links 18 within a second deterministic domain 26b
based on second different deterministic constraints established by
the network manager device 24b and sent to each of the
deterministic network interface circuits 22 (e.g., 22k, 22l, 22m,
etc.) establishing the deterministic links 18 in the deterministic
domain 26b.
[0033] Although not shown in FIG. 2, the deterministic domain 26b
of the deterministic data network 20 continues with peer
deterministic network interface circuits 22 receiving the transport
layer packets 16 deterministically transmitted by the switching
devices "5", "6", and "7" containing the respective deterministic
network interface circuits 22k, 22l, and 22m.
[0034] FIG. 2 also illustrates that the deterministic data network
20' includes an intermediate host device 10'' that can
deterministically reorder the transport layer packets 16 between
the deterministic domain 26a and deterministic domain 26b, based on
transport sequence identifiers within the received transport layer
packets 16, described in further detail below.
[0035] As illustrated in FIG. 1A and FIG. 2 and described in
further detail below, the transport layer 14 executed by the
processor circuit 12 in the source host device 10 is configured for
receiving a flow of application data originated by an executable
application (34 of FIG. 3): the transport layer 14 executed in the
source host device 10 is configured for generating transport layer
packets 16 that contain one or more portions of the application
data; the transport layer 14 also is configured for generating and
inserting into each transport layer packet 16 a corresponding
transport sequence identifier 30 that uniquely identifies a
corresponding position of the transport layer packet 16 relative to
a transport order of the transport layer packets 16. The transport
layer 14 also can generate and insert into each transport layer
packet 16 a transport flow identifier (e.g., "A1") 32 associated
with the flow of application data from the executable application
(34 of FIG. 3). The transport layer 14 can generate each transport
layer packet 16 according to the deterministic constraints
established by the network manager device 24, for example
generating within a period of time "T" no more than the maximum
number of data packets "N" each having no more than a maximum
packet size "F" (minus any data link layer header information added
by a deterministic network interface circuit 22, described
below).
[0036] Hence, the transport layer 14 executed in the source host
device 10 (also referred to herein as the "source transport layer")
can generate a sequence of transport layer packets 16, containing
the flow of application data, according to the deterministic
constraints established by the network manager device 24, and where
each transport layer packet 16 specifies a corresponding transport
sequence identifier 30. As described in further detail below, the
transport layer 14 also can cause the transmitting deterministic
network interface circuits 22 (e.g., 22a and/or 22b of FIGS. 1A-1G;
22e and/or 22f of FIGS. 1H-1J and/or FIG. 2) to deterministically
retrieve the transport layer packets 16, in the transmit order,
from a transmit buffer circuit (e.g., 36 of FIG. 3) for
deterministic transmission across the respective deterministic
links 18.
[0037] As illustrated in FIG. 2, the source transport layer 14 also
can generate coded packets (e.g., "A1.C1", "A1.C2", "A1.C3",
"A1.C4", etc.) associated with the transport layer packets 16, and
insert the coded packets into the transport layer transmit buffer
circuit 36 for error-protected transmission of the transport layer
packets 16. For example the source transport layer 14 can generate
the coded packet "A1.C1" as a "1+1" network-coded result of the
transport layer packets "A1.004" and "A1.005", enabling a
destination to recover the transport layer packet "A1.004" using
the transport layer packet "A1.005" and the coded packet "A1.C1".
The coded packet (e.g., "A1.C1") can be queued for transmission
before the associated protected transport layer packets (e.g.,
"A1.004" and "A1.005"), enabling immediate recovery if one of the
protected transport layer packets is lost.
[0038] As illustrated in Figures 1A and 2, each deterministic
network interface circuit 22 comprises a transmit/receive buffer
circuit 40 and a transmit/receive gate circuit 42. The
transmit/receive buffer circuit 40 (e.g., in the deterministic
network interface circuits 22a, 22b, 22e, 22f, 22g, 22h, and
22k-22m) is configured for storing "transmit" data to be
transmitted by the corresponding transmit/receive gate circuit 42
as a link layer data packet (e.g., 44a of FIG. 1B) according to the
deterministic constraints established by the network manager device
24; the transmit/receive buffer circuit 40 also can be configured
(e.g., in the deterministic network interface circuits 22c, 22d,
22g, 22h, 22i, 22j) for storing "receive" data as the link layer
data packet (e.g., 44a of FIG. 1B) is received by the corresponding
transmit/receive gate circuit 42 according to the deterministic
constraints established by the network manager device 24.
Alternately, the transmit/receive buffer circuit 40 can be
implemented based on separating the transmit buffer circuit from
the corresponding receive buffer circuit, and the transmit/receive
gate circuit 42 can be implemented based on separating the transmit
gate circuit from the corresponding receive gate circuit.
[0039] Hence, the transport layer 14 in the source host device 10
can cause any one of the deterministic network interface circuits
22a and/or 22b to deterministically retrieve a transport layer 14
from the transport layer transmit buffer circuit 36, described in
further detail below with respect to FIGS. 4A and 4B. Each
transmitting deterministic network interface circuit 22, however,
controls the actual time instance that it deterministically fetches
the next transport layer packet 16 from the transport layer
transmit buffer circuit 36, without the knowledge or control of the
transport layer 14. In particular, while the transport layer 14
causes the deterministic retrieval of the transport layer packets
16 from the transport layer transmit buffer circuit 36 (e.g., based
on deciding multiple deterministic network interface circuits 22
are needed for deterministic transport of the transport layer
packets 16, establishing at least a portion of the deterministic
network parameters required for pre-fetching the transport layer
packet 16 before the next transmission instance, triggering the
deterministic network interface circuits 22 when to begin the
process of fetching the transport layer packets 16, etc.), the
transport layer 14 is not necessarily part of the deterministic
data network 20, and therefore is not aware of the precise
transmission instance executed by any of the transmitting
deterministic network interface circuits 22. Hence, while the
transport layer 14 can cause the deterministic retrieval of the
transport layer packets 16 by the deterministic network interface
circuits 22, the actual retrieval of a transport layer packet 16 is
initiated by a deterministic network interface circuit 22 and not
the transport layer 14.
[0040] Hence, as illustrated in FIG. 1A, the deterministic network
interface circuit 22b can deterministically retrieve (from the
transport layer transmit buffer circuit 36 illustrated in FIG. 3)
the transport layer packet 16 having the transport sequence
identifier "001" 30 at a first time instance (126 of FIG. 5) that
precedes its corresponding transmission instance (84 of FIG. 5) on
the "TSN Link 2" 18 (without knowledge or control by the transport
layer 14 in the source host device 10), whereas the deterministic
network interface circuit 22a can deterministically retrieve from
the transport layer transmit buffer circuit 36 the next transport
layer packet 16 having the transport sequence identifier "002" 30
(without knowledge or control by the transport layer 14 in the
source host device 10). As described in further detail below, the
transport sequence identifiers 30 in the transport layer packets 16
enable a destination transport layer 14 (e.g., within the
destination host device 10') to recover the transmit order
established by the transport layer 14 in the source host device 10,
following the deterministic transmission across the deterministic
links 18, regardless of order of reception thereof by the
destination transport layer 14 in the destination host device 10'
or the intermediate host device 10''. FIG. 3 illustrates an example
implementation of any one of the devices 10, 10', 10'', 24, 28,
and/or 38 of FIGS. 1A-1J and/or FIG. 2, according to an example
embodiment. Each apparatus 10, 10', 10'', 24, 28, and/or 38 is a
physical machine (i.e., a hardware device) configured for
implementing network communications with other physical machines
via the deterministic data network 20, 20', and/or another data
network (e.g., a local area network (LAN) and/or a Wide Area
Network (WAN) such as the Internet). The term "configured for" or
"configured to" as used herein with respect to a specified
operation refers to a device and/or machine that is physically
constructed and arranged to perform the specified operation.
Depending on implementation, each device 10, 10', 10'', 24, 28,
and/or 38 can include a processor circuit 12, a device interface
circuit 52 and/or 22, a memory circuit 54 interconnected by a
system bus (e.g., PCI Express (PCIe)) 58, and a power supply 60
(e.g., battery, plug-in, etc.).
[0041] The device interface circuit 22 and/or 54 can include
mechanical, electrical, and signaling circuitry for communicating
data with other device interface circuits 22 and/or 54; for
example, each device interface circuit 22 and/or 54 can include one
or more distinct physical layer transceivers for communication with
any one of the other devices of FIG. 1 or 2 as described herein;
for example, the device interface circuit 52 can be implemented as
a ten Gigabit (10 GB) Ethernet (10GBASE-T) link layer transceiver
configured for establishing a data link 56 with any one of the 10,
10', 10'', 24, 28, and/or 38 via a non-deterministic data
connection (not shown); for example, the non-deterministic data
connection could exist within the physical data network (e.g., LAN
and/or WAN) that is used to deploy the deterministic data network
20 or deterministic data network 20', where data links that are
having unreserved (i.e., "free") intervals that are not reserved
for deterministic transport can be used for non-deterministic data
connections. Alternately, one or more of the 10, 10', 10'', 24, 28,
and/or 38 (e.g., the host devices 10, 10' and/or 10'') can include
both the device interface circuit 52 for non-deterministic
communications (e.g., with the network manager device 24) and
plural deterministic network interface circuits 22 for
deterministic communications as described herein.
[0042] As described in further detail below, the device interface
circuit 52 can include a ASIC 130 and a transmit buffer circuit
132.
[0043] Any one of the devices 10, 10', 10'', 24, 28, and/or 38 also
can be configured for a different type of deterministic link 18 or
data link 56, as appropriate (e.g., a wired or wireless link, an
optical link, etc.).
[0044] The processor circuit 12 can be configured for executing any
of the operations described herein, and the memory circuit 54 can
be configured for storing any data or data packets as described
herein. For example, the processor circuit 12 and the memory
circuit 54 implemented in the source host device 10, 10', 10'' or
the network manager device 24 can have a different implementation
than the processor circuit 12 and memory circuit 54 implemented in
any one of the deterministic network interface circuits 22, the TOR
switching device 28, and/or the switching device 38. The processor
circuit 12 can be implemented as any one of a microprocessor
circuit, a multi-core processor circuit, an application-specific
integrated circuit (ASIC), etc.
[0045] Any of the disclosed circuits of the devices 10, 10', 10'',
24, 28, and/or 38 (including the device interface circuit 22 or 52,
the processor circuit 12, the memory circuit 54, and their
associated components) can be implemented in multiple forms.
Example implementations of the disclosed circuits include hardware
logic that is implemented in a logic array such as a programmable
logic array (PLA), a field programmable gate array (FPGA), or by
mask programming of integrated circuits such as one or more
application-specific integrated circuits (ASICs). Any of these
circuits also can be implemented using a software-based executable
resource that is loaded into the apparatus (e.g., via a device
interface circuit such as an Ethernet connector, a Universal Serial
Bus (USB) device, or some other machine-readable medium interface
such as a CD-ROM drive) and executed by a corresponding internal
processor circuit such as a microprocessor circuit (not shown) and
implemented using one or more integrated circuits, where execution
of executable code stored in an internal memory circuit (e.g.,
within the memory circuit 54) causes the integrated circuit(s)
implementing the processor circuit to store application state
variables in processor memory, creating an executable application
resource (e.g., an application instance) that performs the
operations of the circuit as described herein. For example, the
memory circuit 54 can be configured for storing application state
variables for a transport layer process 14, an executable
application process 34, an operating system process 62, and/or a
device manager process 64; in some cases certain processes can be
combined, for example the transport layer process 14 and the device
manager process 64 can be combined within the operating system
process 62. Example data structures 66 stored in the memory circuit
54 can include the transport layer transmit buffer circuit 36
storing the transport layer packets 16 awaiting retrieval by the
deterministic network interface circuits 22, a transport layer
receive buffer circuit 68 configured for storing received transport
layer packets 16 from a receiving deterministic network interface
circuit 22 (e.g., 22c, 22d, 22i, 22j), an identified flow of
application data 70 generated by the executable application 34,
device manager parameters 72 including line card allocation
parameters and associated deterministic constraints established for
deterministic transmission by the deterministic network interface
circuit 22a and/or 22b, etc.
[0046] Hence, use of the term "circuit" in this specification
refers to both a hardware-based circuit implemented using one or
more integrated circuits and that includes logic for performing the
described operations, or a software-based circuit that includes a
processor circuit (implemented using one or more integrated
circuits), the processor circuit including a reserved portion of
processor memory for storage of application state data and
application variables that are modified by execution of the
executable code by a processor circuit. The memory circuit 54 can
be implemented, for example, using a non-volatile memory such as a
programmable read only memory (PROM) or an EPROM, and/or a volatile
memory such as a DRAM, etc.
[0047] Further, any reference to "outputting a message" or
"outputting a packet" (or the like) can be implemented based on
creating the message/packet in the form of a data structure and
storing that data structure in a non-transitory tangible memory
medium in the disclosed apparatus (e.g., in a transmit buffer). Any
reference to "outputting a message" or "outputting a packet" (or
the like) also can include electrically transmitting (e.g., via
wired electric current or wireless electric field, as appropriate)
the message/packet stored in the non-transitory tangible memory
medium to another network node via a communications medium (e.g., a
wired or wireless link, as appropriate) (optical transmission also
can be used, as appropriate). Similarly, any reference to
"receiving a message" or "receiving a packet" (or the like) can be
implemented based on the disclosed apparatus detecting the
electrical (or optical) transmission of the message/packet on the
communications medium, and storing the detected transmission as a
data structure in a non-transitory tangible memory medium in the
disclosed apparatus (e.g., in a receive buffer). Also note that the
memory circuit 54 can be implemented dynamically by the processor
circuit 12, for example based on memory address assignment and
partitioning executed by the processor circuit 12.
[0048] FIGS. 4A-4C illustrate an example method of a transport
layer providing deterministic transport of transport layer packets
across multiple deterministic links, according to an example
embodiment.
[0049] The operations described with respect to any of the Figures
can be implemented as executable code stored on a computer or
machine readable non-transitory tangible storage medium (i.e., one
or more physical storage media such as a floppy disk, hard disk,
ROM, EEPROM, nonvolatile RAM, CD-ROM, etc.) that are completed
based on execution of the code by a processor circuit implemented
using one or more integrated circuits; the operations described
herein also can be implemented as executable logic that is encoded
in one or more non-transitory tangible media for execution (e.g.,
programmable logic arrays or devices, field programmable gate
arrays, programmable array logic, application specific integrated
circuits, etc.). Hence, one or more non-transitory tangible media
can be encoded with logic for execution by a machine, and when
executed by the machine operable for the operations described
herein.
[0050] In addition, the operations described with respect to any of
the Figures can be performed in any suitable order, or at least
some of the operations can be performed in parallel. Execution of
the operations as described herein is by way of illustration only;
as such, the operations do not necessarily need to be executed by
the machine-based hardware components as described herein; to the
contrary, other machine-based hardware components can be used to
execute the disclosed operations in any appropriate order, or
execute at least some of the operations in parallel.
[0051] Referring to FIG. 4A, the processor circuit 12 executing the
source host transport layer 14 in the source host device 10 is
configured for determining in operation 80 the deterministic
attributes and/or constraints that are required for an identified
flow of application data 70 originated by the executable
application 34 in the source host device 10. Example deterministic
attributes can include identifying the destination host device 10'
(e.g., by host name and/or
[0052] Internet Protocol (IP) address, etc.), identifying a minimum
Quality of Service (QoS) required for packet delivery at the
destination host device 10', expressed for example as a prescribed
minimum bandwidth, an overall jitter below a prescribed maximum
jitter variation, a packet delivery ratio, a latency below a
prescribed maximum latency, etc. The transport layer 14 (executed
by the processor circuit 12 in the source host device 10) also can
have access to available deterministic attributes of one or more
deterministic links 18 established by a deterministic network
interface circuit 22.
[0053] The transport layer 14 (executed by the processor circuit 12
in the source host device 10) in operation 82 also can determine
for each deterministic network interface circuit 22 a pre-fetch
interval (74 of FIG. 5) for each deterministic network interface
circuit 22 coupled to the source host device 10 for deterministic
transmission of transport layer packets 16. As illustrated in FIG.
5, the transport layer 14 can determine a retrieval latency 76 for
a corresponding deterministic network interface (e.g., 22a, 22b,
22e, and/or 220 to retrieve the corresponding transport layer
packet 16 from the transport layer transmit buffer circuit 36, and
a transmit queuing latency 78 for the corresponding deterministic
network interface (e.g., 22a, 22b, 22e, and/or 22f) to queue the
corresponding transport layer packet for the corresponding
deterministic transmission at the scheduled transmission instance
84. The transport layer 14 can determine the transmit queuing
latency 78, for example based on a query to the corresponding
deterministic network interface circuit 22, and/or by accessing the
pre-fetch interval 74 from the device manager parameters 72 stored
in the local memory circuit 54.
[0054] Hence, the transport layer 14 (executed by the processor
circuit 12 in the source host device 10) can cause each
deterministic network interface circuit 22 associated with the
source host device 10 to deterministically retrieve, at a
corresponding retrieval instance 126, each transport layer packet
16 from the transport layer transmit buffer circuit 36 by the
pre-fetch interval 74 preceding the corresponding deterministic
transmission at the scheduled transmission instance 84, based on
determining in operation 84 the corresponding pre-fetch interval
74, and sending in operation 86 a request to the device manager 64
to allocate a plurality of deterministic network interface circuits
22 (e.g., 22a and 22b, or 22e and 22f, etc.) for deterministic
transport of the transport layer packets 16 (using the transport
flow identifier "A1" 32) according to the deterministic attributes
required for the identified flow of application data 70. As
described below, each deterministic network interface circuit 22
can initiate retrieval of a transport layer packet by generating
and outputting a "more" message 100 at the corresponding retrieval
instance 126; in other words, each deterministic network interface
circuit can define initiation of the next retrieval instance 126 by
transmission of the "more" message 100. The "more" message 100 also
is referred to herein as a request message.
[0055] The transport layer 14 in operation 86 also can determine
that a single one of the deterministic links 18 has insufficient
resources for deterministic transport of the transport layer
packets 16 to the destination transport layer 14 (executed in the
source host device 10 or the intermediate host device 10''), and in
response the transport layer packet 16 can specify in the request
to the device manager 64 that multiple deterministic network
interface circuits 22 are required for the deterministic transport
of the transport layer packets 16.
[0056] The device manager 64 executed by the processor circuit 12
in the source host device 10 (i.e., the source host manager) in
operation 88 can coordinate with the network manager device 24
(and/or 24a and 24b of FIG. 2, as appropriate), for establishment
of end-to-end deterministic links 18 for the transport layer packet
16 from the source host device 10 to the destination host device
10' via the deterministic data network 20 (or the deterministic
data network 20' of FIG. 2). The network manager device 24 (and/or
24a and 24b of FIG. 2) in operation 90 can coordinate with the
downstream switching devices 38, any intermediate host device 10''
(as appropriate), and the destination host device 10', for
establishment of the plural deterministic links 18 for end-to-end
deterministic transmission via the deterministic links 18 of the
transport layer packets 16 from the source host device 10 to the
destination host device 10', according to the required
deterministic constraints. For example, the network manager device
24a of FIG. 2 can send instructions to the deterministic network
interface circuits 22e, 22g, and 22i for the establishment in the
deterministic domain 26a of a first deterministic path (comprising
"TSN link 1" 18 and "TSN link 1'" 18) having first deterministic
constraints for the transport layer packets 16 having the transport
flow identifier "Al" 32; the network manager device 24a of FIG. 2
also can send instructions to the deterministic network interface
circuits 22f, 22h, and 22j for the establishment in the
deterministic domain 26a of a second deterministic path (comprising
"TSN link 2" 18 and "TSN link 2'" 18) having second different
deterministic constraints for the transport layer packets 16 having
the transport flow identifier "A1" 32. The network manager device
24a also can notify the intermediate host device 10'' of the first
and second deterministic paths for the transport layer packets 16
having the transport flow identifier "A1" 32. As apparent from the
foregoing, the device manager 64 in the intermediate host device
10'' can coordinate with the network manager device 24b to
establish deterministic paths in the deterministic domain 26b;
alternately, the network manager device 24a and network manager
device 24b can communicate to establish the deterministic transport
of the transport layer packets 16 across the respective
deterministic domains 26a and 26b via the intermediate host device
10''.
[0057] The network manager device 24 in operation 90 also can send
an acknowledgement to the device manager 64 specifying the plural
deterministic links 18 are established for the transport layer
packets 16 identified by the transport sequence identifier "A1" 30,
including for example for each identified deterministic network
interface circuit 22 the prescribed transmission period of time
"T", the maximum number of "N" data packets having a maximum size
"F" that can be transmitted during the transmission time period
"T", and the repeat interval for the repeating schedule. The device
manager 64 executed in the source host device 10 can notify the
transport layer 14 of the identified deterministic network
interface circuits 22 and the supplied parameters (note that the
transport layer 14 need not be aware of the actual scheduled
starting transmission time "t_TSN" 84).
[0058] The transport layer 14 executed in the source host device 10
in operation 92 also can allocate the size of the transport layer
transmit buffer circuit 36 in the memory circuit 54 based on
determining the maximum latency interval (L_MAX) across the
deterministic links 16 from the source host device 10 to the "next"
transport host (e.g., the intermediate host device 10'' or the
destination host device 10'), the maximum number of transport layer
packets 16 that can be transmitted within the maximum latency, and
the maximum size "F" of the transport layer packets 16. The maximum
latency interval (L_MAX) across the deterministic links refers to
the maximum time interval that may be needed for the transport
layer 14 in the destination host device 10' to recover if an
out-of-sequence packet is lost during transmission, as the source
transport layer 14 executed in the source host device 10 does not
specifically control which transport layer packet 16 a
deterministic network interface circuit 22 should retrieve from the
transport layer transmit buffer circuit 36, nor does the source
transport layer 14 specifically control the scheduled transmission
84 by the transmit/receive gate circuit 42 of a given deterministic
network interface circuit 22. Hence, the maximum latency interval
(L_MAX) refers to the maximum amount of time a transport layer 14
must store successive transport layer packets 16 (i.e., having
adjacent transport sequence identifiers 30) in case the different
transport layer packets 16 are out of order and an out-of-order
transport layer packet 16 needs to be reordered and/or
retransmitted (if permitted according to the link-layer protocol
executed by the deterministic link 18).
[0059] As described in further detail below, in FIG. 1A the
deterministic network interface circuit 22b deterministically
retrieves the transport layer packet 16 having the transport
sequence identifier "001" 30 and stores in its transmit/receive
buffer circuit 40 to await deterministic transmission at its next
scheduled transmission opportunity, and the deterministic network
interface circuit 22a deterministically retrieves the transport
layer packet 16 having the transport sequence identifier "002" 30;
in FIG. 1B the deterministic network interface circuit 22a
deterministically transmits at event "t=t1" 46b the link layer data
packet 44a containing the transport layer packet 16 having the
transport sequence identifier "002" 30 while the deterministic
network interface circuit 22b waits for its next scheduled
transmission opportunity (at event "t=t4" 46e of FIG. 1E) before it
can transmit the transport layer packet 16 having the transport
sequence identifier "001" 30; hence, the maximum latency interval
(L_MAX) is the maximum time the transport layer 14 in the source
host device 10 must wait before it can clear a retrieved transport
layer 14 from its queue (L_MAX=t4-t0). Hence, the transport layer
14 in operation 92 can be configured for allocating the size of the
transport layer transmit buffer circuit 36 in the memory circuit 54
based on determining the maximum latency interval (L_MAX) across
all the allocated deterministic links 18 for the identified flow
"Al" 32, the maximum number of transport layer packets 16 that can
be transmitted across all the allocated deterministic links 18
during the maximum latency, and the maximum size "F" of the
transport layer packets 16. Similar allocations can be performed by
the transport layer 14 for the transport layer receive buffer
circuit 68, described below, for storage of received transport
layer packets 16 while awaiting other transport layer packets 16
for reordering into the proper transmit sequence according to the
transport sequence identifier 30.
[0060] Referring to FIG. 4B, the transport layer 14 executed in the
source host device 10 in operation 94 receives the flow of
application data packets 70 originated by the executable
application 34; for example, the transport layer 14 can receive an
alert (e.g., metadata, a descriptor, etc.) indicating the storage
of the identified flow of application data 70 by the executable
application 34 in the memory circuit 54, enabling the transport
layer 14 to fetch an ordered sequence of the portions of the
application data (e.g., as application data "chunks") from the
memory circuit 54. Alternately, the executable application 34
and/or the operating system 62 can supply the identified flow of
application data 70 as a data flow to the transport layer 14, for
example where the transport layer 14 is executed in a hardware
circuit that is distinct from the executable application 34 (e.g.,
multi-core processor, distinct ASICs, etc.). The transport layer 14
can receive the identified flow of application data 70 as a block
of stored application data, an application data burst, a steady
stream of application data "chunks", etc. Hence, the transport
layer 14 can receive the flow of application data 70 as a sequence
of portions of the application data from the executable application
34 executed locally by the processor circuit 12.
[0061] The transport layer 14 executed in the source host device 10
in operation 96 is configured for assembling one or more
application data chunks into a single transport layer packet 16
having an optimized packet size based on the maximum size "F"
determined for the deterministic links 18. The transport layer 14
in operation 96 also can generate a transport flow identifier
(e.g., "A1") 32 associated with the identified flow of application
data 70, for example to distinguish from another application flow
generated by the same executable application (e.g., for a different
destination, different content type, different sensor source,
etc.). The transport layer 14 in operation 96 also can maintain a
sequence counter for the identified flow of application data
[0062] "A1" 70 for tracking the sequence of the transport layer
packets 16 to be transported across the deterministic links 18. The
transport layer 14 in operation 96 inserts the transport flow
identifier 32 and the corresponding transport sequence identifier
30 into the transport layer packet 16, and stores the generated
transport layer packet 16 into the transport layer transmit buffer
circuit 36. As described previously, the transport sequence
identifier 30 enables a receiving transport layer 14 (e.g.,
executed in the destination host device 10' or an intermediate host
device 10'') to reorder any received transport layer packets 16
into the appropriate transmit order to correct any mis-ordering due
to different transmission schedules, different latencies, link
layer transmission parameters, etc., across the deterministic links
18.
[0063] The transport layer 14 executed in the source host device 10
in operation 98 optionally can send a trigger message to the
allocated deterministic network interface circuits 22 (e.g., 22a,
22b of FIGS. 1A-1G; 22e, 22f of FIGS. 1H-1J and FIG. 2) indicating
the availability of the transport layer packets 16 for the
identified flow of application data. Each deterministic network
interface circuit 22 can respond to the trigger message by
deterministically retrieving a corresponding transport layer packet
16, in the transmit order, from the transport layer transmit buffer
circuit 36 no later than the retrieval instance 126, i.e.,
initiating retrieval by at least the pre-fetch interval 74 before
the next scheduled transmission instance 84 by the transmit/receive
gate circuit 42 for the corresponding deterministic network
interface circuit 22. Hence, any one or more of the operations 80,
82, 86, 88, 90, 92, 94, 96, and/or 98 by the transport layer 14
cause the deterministic network interface circuit 22 to
deterministically retrieve the transport layer packets 16, in the
transmit order, for deterministic transmission across the
respective deterministic links 18.
[0064] Each deterministic network interface circuit 22 in operation
99 can deterministically fetch the next transport layer packet 16
by fetching the transport layer packet 16 by at least the pre-fetch
interval 74 before the next scheduled transmission instance 84
based on generating and outputting a "more" message 100, described
in further detail below with respect to FIG. 1B. As illustrated
with respect to FIGS. 1A-1G, the deterministic network interface
circuits 22a and 22b can fetch the next transport layer packet 14
via the system bus 58 (e.g., using the "more" message 100 for
executing a memory-read operation from an identified location in
the memory circuit 54; alternately with respect to FIGS. 1H-1J and
FIG. 2, the deterministic network interface circuits 22e and 22f
can fetch the next transport layer packet 16 via the TOR switching
device 28 and the data link 56; the device interface circuit 52
executed in the source host device 10 of FIGS. 1H-1J and FIG. 2 can
retrieve the next transport layer packet 16 from the transport
layer transmit buffer circuit 36 on behalf of the deterministic
network interface circuits 22e and 22f (e.g., the "more" message
100 requesting a remote memory read operation of the memory circuit
54 by the deterministic network interface circuits 22e and 22f, or
the "more" message 100 requesting that the device interface circuit
52 and/or the processor circuit 12 fetches the next transport layer
packet 16 as a message-initiated host transfer).
[0065] Hence, each "more" message 100 output by a deterministic
network interface circuit 22 defines or establishes the next
corresponding retrieval instance 126. The "more" message 100 can be
implemented as one of a remote memory read request (enabling the
deterministic network interface circuit 22 to directly fetch the
next transport layer packet 16 from the transport layer transmit
buffer circuit 36 in the memory circuit 54), and/or the "more"
message 100 can be implemented as a message-initiated host transfer
request that causes the device interface circuit 52/and/or the
processor circuit 12 to fetch the next transport layer packet 16,
from the transport layer transmit buffer circuit 36, on behalf of
the deterministic network interface circuit 22; alternately, the
message-initiated host transfer can include the transport layer 14
(executed by the processor circuit 12) storing in advance different
transport layer packets 16 in a transport buffer circuit 132 in the
device interface circuit 52, enabling the device interface circuit
52 to output the next transport layer packet 16, from its internal
transmit buffer circuit 132, in response to a received "more"
message 100 via the data link 56. As apparent from the foregoing,
execution of the "more" message 100 at the retrieval instance 126
as a remote memory read request can minimize the retrieval latency
76 since the hardware associated with the deterministic network
interface circuit 22 is used to access the memory circuit 54 of the
source host device 10; execution of the "more" message 100 at the
retrieval instance 126 as a message-initiated host transfer request
may provide more security for the source host device 10 (by
limiting access to the memory circuit 54), but can increase the
retrieval latency 76 based on competing resource requirements in
the processor circuit 12 and/or the device interface circuit
52.
[0066] Each deterministic network interface circuit 22 (e.g., 22a,
22b, 22e, 22f) in operation 99 also can add its own link-layer
stream identifier 48 and link-layer sequence identifier 50 to each
link layer data packet 44 prior to queuing in its corresponding
transmit/receive buffer circuit 40. Hence, the transmit/receive
gate circuit 42 in each deterministic network interface circuit 22
waits for its next corresponding scheduled transmission instance 84
before transmitting the link layer data packet 44 stored in its
transmit/receive buffer circuit 40. As described previously, each
scheduled transmission instance 84 is established by the network
manager device 24 as part of the deterministic sequence of
transmissions, for example according to TSN, AVB, DetNet, etc.
[0067] As illustrated in FIG. 1A and FIG. 1H, at event 46a at time
t=t0 the deterministic network interface circuit 22a (or the
deterministic network interface circuit 22e in FIG. 1H) stores the
transport layer packet 16 having the transport sequence identifier
"002" 30 in its corresponding transmit/receive buffer circuit 40,
after the deterministic network interface circuit 22b (or the
deterministic network interface circuit 22f in FIG. 1H) has
previously stored the transport layer packet 16 having the
transport sequence identifier "001" 30 in its corresponding
transmit/receive buffer circuit 40. A deterministic network
interface circuit 22 in operation 102 of FIG. 4B deterministically
transmits its stored link layer data packet 44 (containing the
transport layer packet 16) at the scheduled transmission instance
84 via the deterministic link 18 to its corresponding downstream
deterministic network interface circuit 22. As illustrated in FIGS.
1B and 1I, at event 46b at time t=t1 (after event 46a) the
transmit/receive gate circuit 42 of the deterministic network
interface circuit 22a (or 22e) initiates its scheduled transmission
84 at its transmission instance of a link layer data packet 44a
that contains the transport layer packet 16 having the transport
sequence identifier "002" 30 and comprising a link-layer (e.g., TSN
layer) stream identifier "TSN1" 48 and a link-layer sequence
identifier "001" 50; the transmit/receive gate circuit 42 of the
downstream peer deterministic network interface circuit 22c (or
22i) at event 46b at time t=t1 deterministically receives the link
layer data packet 44a (within a prescribed deterministic latency)
at its reception instance coinciding with the transmission
instance, and in response to reception thereof sends an
acknowledgement to the deterministic network interface circuit 22a
(or 22e) that causes the deterministic network interface circuit
22a (or 22e) in operation 104 and 106 to send a "more message" 100
to the transmitting transport layer 14. As apparent from FIG. 1B,
for example, the transport sequence identifier 30 (generated by the
transport layer 14) is distinct from the link-layer sequence
identifier 50 generated by the deterministic network interface
circuit 22.
[0068] If in operation 104 the deterministic network interface
circuit 22a (or 22e) does not receive the acknowledgement following
transmission of the link layer data packet 44a, the deterministic
network interface circuit 22a (or deterministic network interface
circuit 22e) optionally can retransmit, as appropriate according to
the deterministic constraints established by the network manager
device 24 and the link-layer protocol in use (e.g., according to a
wireless deterministic protocol such as 6TiSCH).
[0069] The deterministic network interface circuit 22a (or 22e) in
operation 106 transmits a "more" message 100 that can specify the
transport sequence identifier ".002" 30 (and optionally the
transport flow identifier 32) of the transport layer packet 16,
indicating successful deterministic transmission of the transport
layer packet 16; the "more" message 100 optionally can specify a
transmitter identifier (e.g., "Q1" for the deterministic network
interface circuit 22a in FIG. 1B, "SW1" for the deterministic
network interface circuit 22e in FIG. 11). The "more" message 100
also can specify the associated deterministic constraints, for
example the maximum packet size "F", and the maximum number of data
packets "N" that can be transmitted on the corresponding
deterministic link 18 within the period of time "T", enabling the
retrieval of the next transport layer packet 16 having the correct
packet size via remote memory read or message-initiated host
transfer. The transport layer 14, in response to receiving in
operation 108 the "more" message 100, can mark the associated
transport layer packet 16 (having the identified transport sequence
identifier ".002" 30 specified in the "more" message 100) as
successfully transmitted and clear (i.e., discard) the transport
layer packet 16 having the transport sequence identifier ".002" 30
from the transport layer transmit buffer circuit 36.
[0070] Referring to FIGS. 1C and 1J, at event "t=t2" 46c (or event
"t=t2'" 46c' of FIG. 1J) (after event "t=t1" 46b) the deterministic
network interface circuit 22a (or 22e), after having transmitted
the "more" message 100, can repeat operations 100, 102, 104, and
106 for retrieval of the next transport layer packet 16 stored in
the transport layer transmit buffer circuit 36 by at least
pre-fetch interval 74 before the next scheduled transmission
instance 84, namely the transport layer packet 16 having the
transport sequence identifier ".003" 30; the deterministic network
interface circuit 22a (or 22e) at event "t=t2" 46c (or event
"t=t2'" 46c' of FIG. 1J) in operation 99 also can fetch transport
message metadata 110 associated with the retrieved transport layer
packet 16. In an alternate embodiment the transport layer 14 can
repeat operation 98 in response to receiving the "more" message 100
in operation 108, in order to actively cause the deterministic
network interface circuit 22a (or 22e) to retrieve the next
transport layer packet 16 from the transport layer transmit buffer
circuit 36; this alternate embodiment can be preferred to avoid
buffer underflow where the deterministic network interface circuit
22 would attempt to access the transport layer transmit buffer
circuit 36 if empty.
[0071] Referring to FIG. 4C, the destination transport layer 14
executed by the destination host device 10' (or the intermediate
host device 10'' in FIG. 2) in operation 112 can allocate its
corresponding transport layer receive buffer circuit 68 based on
the maximum latency expected across the deterministic links 18, as
described previously with respect to operation 92. The destination
transport layer 14 (based on coordinating with the network manager
device 24 via the device manager 64) can allocate its corresponding
transport layer receive buffer circuit 68 in its local device
manager 64 based on determining the maximum latency interval
(L_MAX) across all the allocated deterministic links 18 for the
identified flow "A1" 32, the maximum number of transport layer
packets 16 that can be transmitted across all the allocated
deterministic links 18 during the maximum latency, and the maximum
size "F" of the transport layer packets 16.
[0072] As described previously with respect to FIGS. 1B and 1I, the
transmit/receive gate circuit 42 of the downstream peer
deterministic network interface circuit 22c (or 22i) at event 46b
at time t=1 deterministically receives the link layer data packet
44a (within a prescribed deterministic latency from the scheduled
transmission instance 84), and in response the downstream peer
deterministic network interface circuit 22c (or 22i) removes the
link layer header (specifying the link-layer stream identifier 48
and the link-layer sequence identifier 50) and forwards the
received transport layer packet 16 (specifying the transport
sequence identifier "002" 30) to the transport layer 14, for
example based on storing the received transport layer packet 16 in
the transport layer receive buffer circuit 68 with receive message
metadata 114 that notifies the receiving transport layer 14 of the
received transport layer packet 16. Hence, the receiving transport
layer 14 can respond to receiving the transport layer packet 16 in
operation 116 by determining whether the corresponding transport
sequence identifier 30 indicates the transport layer packet 16 is
out-of-sequence, where the transport layer receive buffer circuit
68 is missing a transport layer packet 16 specifying a prior
transport sequence identifier 30.
[0073] Similar to the transmitting transport layer 14 executed in
the source host device 10, the receiving transport layer 14
executed in the intermediate host device 10'' or the destination
host device 10' can track the received transport sequence
identifiers 30 for the transport layer packets 16 specifying the
transport flow identifier "A1" 32. Hence, the receiving transport
layer 14 can respond to the received transport layer packet 16
(specifying the transport sequence identifier "002" 30) by
determining in operation 118 that it has not received a transport
layer packet 16 specifying the preceding transport sequence
identifier "001" 30. In response to detecting the absence of the
missing transport layer packet, the receiving transport layer 14 in
operation 120 can store the received transport layer packet 16
(specifying the transport sequence identifier "002" 30) in the
transport layer receive buffer circuit 68 while awaiting the
missing transport layer packet 16 specifying the transport sequence
identifier "001" 30. As illustrated in FIG. 1D at event "t=t3" 46d
(or event "t=t2'" 46c' of FIG. 1J) (after event "t=t2" 46c), the
receiving transport layer 14 can store the received transport layer
packet 16 (specifying the transport sequence identifier "002" 30)
in its transport layer receive buffer circuit 68.
[0074] Referring to FIG. 1D, at event "t=t3" 46d the deterministic
network interface circuit 22a is ready to transmit the transport
layer packet 16 specifying the transport sequence identifier "003"
30, while the transmit/receive gate circuit 42 of the deterministic
network interface circuit 22b is still waiting for its next
scheduled transmission instance 84. The receiving transport layer
14 at event "t=t3" 46d continues to store in operation 120 the
received transport layer packet 16 (specifying the transport
sequence identifier "002" 30) in its transport layer receive buffer
circuit 68.
[0075] Referring to FIG. 1E, at event "t=t4" 46e (after event
"t=t3" 46d), the transmit/receive gate circuit 42 of the
deterministic network interface circuit 22b (or 220 in operation
102 initiates its scheduled transmission 84 and deterministically
transmits the link layer data packet 44b containing the transport
layer packet 16 having the transport sequence identifier "001" 30,
the link-layer stream identifier "TSN2" 48, and the link-layer
sequence identifier "001" 50, according to the deterministic
constraints established by the network manager device 24. The
deterministic network interface circuit 22b (or 22f) in operation
106 transmits a "more" message 100 that can specify the transport
sequence identifier ".001" 30 (and optionally the transport flow
identifier 32) of the transport layer packet 16, indicating
successful deterministic transmission of the transport layer packet
16. The transmitting transport layer 14, in response to receiving
in operation 108 the "more" message 100, can mark the associated
transport layer packet 16 (having the identified transport sequence
identifier ".001" 30 specified in the "more" message 100) as
transmitted, and clear (i.e., discard) from the transport layer
transmit buffer circuit 36 the transport layer packet 16 having the
transport sequence identifier ".001" 30.
[0076] The deterministic network interface circuit 22b (or 220,
after having transmitted the "more" message 100, can repeat
operations 100, 102, 104, and 106 for retrieval of the next
transport layer packet 16 stored in the transport layer transmit
buffer circuit 36 by at least the pre-fetch interval 74 before the
next scheduled transmission instance 84, namely the transport layer
packet 16 having the transport sequence identifier ".004" 30.
Referring to FIG. 1F, the deterministic network interface circuit
22b (or 220 at event "t=t5" 46f in operation 99 also can fetch
transport message metadata 110 associated with the retrieved
transport layer packet 16 having the transport sequence identifier
".004" 30.
[0077] Referring to FIG. 1E, the transmit/receive gate circuit 42
of the downstream peer deterministic network interface circuit 22d
(or 22j) deterministically receives the link layer data packet 44b
(within a prescribed deterministic latency from the scheduled
transmission instance 84 at event 46e), and in response the
downstream peer deterministic network interface circuit 22d (or
22j) removes the link layer header and forwards the received
transport layer packet 16 (specifying the transport sequence
identifier "001" 30) to the transport layer 14.
[0078] As illustrated in FIG. 1F, at event "t=t5" 46f the receiving
transport layer 14 receives in operation 116 the transport layer
packet 16 (specifying the transport sequence identifier "001" 30),
and associated receive message metadata 114, and the receiving
transport layer 14 in operation 118 determines reception of the
"missing" transport layer packet 116 (specifying the transport
sequence identifier "001" 30). Hence, the receiving transport layer
14 in operation 122 can receive the "missing" transport layer
packet 116 (specifying the transport sequence identifier "001" 30)
and reorder the received transport layer packets 16 from the
received order (e.g., "002", "001"), into the transmit order (e.g.,
"001", "002").
[0079] In response to reordering the received transport layer
packets 16 in operation 122, the receiving transport layer 14 can
output the transport layer packet 16 in the transmit order in
operation 124, illustrated at event "t=t6" 46g in FIG. 1G. In the
case of the destination host device 10', the destination transport
layer 14 can forward the received transport layer packet 16, in the
transport order, to a higher layer application such as the
executable application 34 for delivery of the recovered identified
flow of application data 70; in the case of an intermediate host
device 10'', the transport layer 14 executed in the intermediate
"fog" host device 10'' can cause the next deterministic interface
circuits (e.g., 22k, 22l, 22m) in operation 98 to deterministically
retrieve the transport layer packets 16 for the next deterministic
domain 26b.
[0080] According to example embodiments, a unique interface can be
established between an executable application in a host device and
deterministic network interface devices in a deterministic network,
without the necessity of the executable application being aware of
the deterministic network. The example embodiments provide a
transport layer that can be installed in any host device and that
can ensure transport layer data packets (and above) can be
recovered following transmission via one or more deterministic
networks, even if the transport layer packets encounter reordering
due to mismatched latencies or unsynchronized portions between the
source application host (executed in the source host device) and
the destination application host (executed in the destination host
device).
[0081] The example embodiments also enable a transport layer to
identify changes in the QoS requirements of the executable
application, or increases in latency encountered within the
transport and/or receive transport layer buffers, and respond
accordingly. For example a source transport layer can recalculate
the required deterministic data links that are required for the
changed QoS requirements, and update the network manager (to
increase or decrease the number of allocated deterministic links)
and change the transmit and/or receive transport layer buffers,
accordingly. Hence, the example embodiments enable a transport
layer to acquire additional deterministic data links in response to
detected increases in latency, or release excess deterministic data
links if the QoS requirements of the executable application are
reduced.
TRANSPORT LAYER IDENTIFYING FAILURE CAUSE AND MITIGATION FOR
DETERMINISTIC TRANSPORT ACROSS DETERMINISTIC LINKS
[0082] In addition to the foregoing, particular embodiments enable
the transport layer to identify a failure cause in a missed
transmission opportunity by one of the deterministic network
interface circuits, where the one deterministic network interface
circuit fails to transmit, at a scheduled transmission instance,
one of the transport layer packets. One cause of a missed
transmission opportunity can be a failed transfer of transport
layer packet output from the apparatus executing the transport
layer (also referred to as a "host device") to the one
deterministic interface circuit, for example due to loss of the
transport layer packet between the host device and the one
deterministic interface circuit; another example of a failed
transfer of the transport layer packet output from the host device
to the one deterministic interface circuit can be that the
transport layer packet fails to arrive at the one deterministic
interface circuit before a scheduled transmission instance on the
deterministic link.
[0083] Another cause of a missed transmission opportunity can be
the host device failing to receive, from the one deterministic
interface circuit, a request message for one of the transport layer
packets; since the host device can be configured to rely on the
request message to provide precise transfer of a transport layer
packet to the one deterministic interface circuit for deterministic
transmission at the scheduled transmission instance, the failure to
receive the request message can results in the transport layer
packet remaining stored in the host device (awaiting the next
request message from one of the deterministic interface circuits).
Hence, failure to de-queue the transport layer can cause an
accumulation in the host device of the transport layer packets,
resulting in a "backlog" or increase in latency of the transport
packets awaiting deterministic transmission among the deterministic
network interface circuits.
[0084] Hence, example embodiments enable the transport layer,
executed in the host device, to determine a cause of failure in a
missed transmission opportunity (detected from a request message),
and selectively execute a corrective action for preventing an
increase in latency of the transport layer packets awaiting
transfer for deterministic transmission among the deterministic
network interface circuits.
[0085] Hence, example embodiments enable the transport layer 14 to
identify or determine a cause of failure in a missed transmission
opportunity by a deterministic network interface circuit 22, and
execute mitigation to ensure continued deterministic transport of
transport layer data packets 16 across the multiple deterministic
links 18, for example based on selectively executing a corrective
action that prevents an increase in latency of the transport layer
packets 16 awaiting transfer to the deterministic network interface
circuits 22.
[0086] As described previously with respect to FIGS. 1H-1J and FIG.
2, the deterministic transport of the transport layer packets 16
across the deterministic link 18 assumes: (1) the source host
device 10 receives each "more" message 100 from a deterministic
network interface circuit 22 via a data link 56 by at least the
pre-fetch interval 74 before the corresponding scheduled
transmission instance 84 (as in FIG. 1I); the (2) source host
device 10 can successfully transfer a transport layer packet 16 to
the deterministic network interface circuit 22 via the data link 56
(as in FIG. 1J); (3) the transport layer packet 16 is successfully
transferred to the deterministic network interface circuit 22
before the expiration of the retrieval latency 76, enabling the
deterministic network interface circuit 22 to queue the received
transport layer packet 16 within the transmit queuing latency 78
for deterministic transmission by the scheduled transmission
instance 84. A failure in any one of these three assumptions can
result in a missed transmission opportunity on the corresponding
deterministic link 18.
[0087] In one embodiment, if a deterministic network interface
circuit 22 having transmitted a "more" message 100 fails to receive
a transport layer packet 16 responsive to the "more" message 100
before the initiation of the transmit queuing latency 78 (i.e., too
late for the scheduled transmission instance 84), or fails to
receive the transport layer packet 16 at all, the deterministic
network interface circuit 22 can generate (within the transmit
queuing latency 78) and transmit at the scheduled transmission
instance 84 a management message (e.g., an Operations,
Administration and Management (OAM) frame) in place of the
transport layer packet 16. Hence, the deterministic network
interface circuit 22 can exploit the otherwise-missed transmission
opportunity by sending an OAM frame to the next-hop transport layer
(executed in the intermediate host device 10'' or the destination
host device 10'). The deterministic network interface circuit 22
can mark the OAM frame as discard-eligible, enabling the next-hop
transport layer to respond to the missed transmission opportunity
for a transport layer packet 16 (i.e., a missed transport layer
packet 16) by executing error correction to recover the missed
transport layer packet 16 using a coded packet, described below,
reporting the missed transport layer packet 16 to a network manager
device 24, and discarding the discard-eligible OAM frame. If the
source host device 10 (or intermediate host device 10'') fails to
receive a "more" message 100 from any one deterministic network
interface circuit 22 for a corresponding scheduled transmission
instance 84, the failure to receive a "more" message 100 can cause
a corresponding failure in de-queuing one of the transport layer
packets 16 from the transport layer transmit buffer circuit 36: the
failure in de-queuing a transport layer packet 16 from the
transport layer transmit buffer circuit 36 can create a "backlog"
in the transport layer packets 16 following the one transport layer
packet 16 that was not de-queued due to the lost "more" message
100.
[0088] According to example embodiments, the transport layer 14 can
determine, from a "more" message 100 specifying any missed
transmission opportunities by the deterministic network interface
circuit 22 on the corresponding deterministic link 18, a cause of
failure in one or more of the missed transmission opportunities,
and selectively execute a corrective action for preventing an
increase in latency of the transport layer packets 16 among the
deterministic network interface circuits 22. As described below,
the transport layer 14 is configured for selectively executing the
corrective action based on marking selected transport layer packets
16 in the transport layer transmit buffer circuit 36 as
discard-eligible (but not any coded packets), and sending a discard
signal to the device interface circuit 52 in response to
determining the cause of failure is a failed reception of a "more"
message 100 previously transmitted by the deterministic network
interface circuit 22. The device interface circuit 52 further is
configured (e.g., by an ASIC 130 executed in the device interface
circuit 52) for discarding from its internal transmit buffer
circuit 132, in response to the discard signal, one of the
discard-eligible transport layer packets having been retrieved by
the device interface circuit 52 from the transport layer transmit
buffer circuit 36, the discarding prior to transfer via the
non-deterministic data link 56 to the one deterministic network
interface circuit 22 in response to the "more" message 100.
[0089] FIGS. 6A and 6B illustrate an example method of identifying
a failure cause in a missed transmission opportunity, and
mitigating against the failure to ensure deterministic transport
across the multiple deterministic data links, according to an
example embodiment. FIG. 7 illustrates an example diagram of the
transport layer in a host device and a deterministic network
interface circuit executing mitigation against a missed
transmission opportunity, according to an example embodiment. The
operations of FIGS. 6A, 6B, and 7 can be executed by the transport
layer 14 executed in any one of the source host device 10 and/or
the intermediate host device 10'', and the associated deterministic
network interface circuits 22 providing the respective
deterministic links 18 for the deterministic transport of the
transport layer packets 16 supplied by the transport layer 14.
[0090] Referring to FIG. 6A, the processor circuit 12 executing the
transport layer 14 in operation 134 can generate the transport
layer packets 16 as described previously with respect to operation
96, except that the transport layer 14 also can generate the coded
packets (illustrated in FIG. 2 as "A1.C1", "A1.C2", "A1.C3",
"A1.C4", etc.) according to a coding ratio that is based on a
number "N" of allocated deterministic network interface circuits
22. For example, if the transport flow "A1" is allocated four (4)
deterministic network interface circuits 22 via respective
switching devices 38 (N=4), the transport layer packet 16 can
generate the coded packets according to a 4:1 coding ratio (N:1).
As described below, the transport layer 14 can reduce the coding
ratio (N:1) in response to determining a failure in one of the
deterministic network interface circuits 22 and reducing the
corresponding number (N=N-1) of allocated deterministic network
interface circuits 22. The transport layer 14 in operation 136 adds
to each packet stored in the transport layer transmit buffer
circuit 36 a "tag" or "flag" that identifies to the ASIC 130 in the
device interface circuit 52 whether the corresponding packet is
discard-eligible. In particular, ASIC 130 can pre-fetch one or more
transport layer packets 16 for storage in the transmit buffer
circuit 132 in anticipation of the next "more" message 100 from a
deterministic network interface circuit 22. The marking of a
redundant packet as discard-eligible by the transport layer 14 in
the transport layer transmit buffer circuit 36 enables the ASIC 130
in the device interface circuit 52, having pre-fetched the
redundant packet from the transport layer transmit buffer circuit
36 into the transmit buffer circuit 132, to "flush" the redundant
packet from the transmit buffer circuit 132 in response to a
discard signal from the transport layer 14, and respond to a "more"
message 100 by transferring the next available packet stored in the
transmit buffer circuit 132.
[0091] Hence, the transport layer 14 in operation 136 marks each
coded packet (e.g., "A1.C1", "A1.C2", "A1.C3", "A1.C4", etc.) as
discard-ineligible (DE=0), and marks each redundant packet in the
transport layer transmit buffer circuit 36 as discard eligible
(DE=1). Examples of a redundant packet in the transport layer
transmit buffer circuit 36 can include a management packet, an OAM
message, a status packet, and the like. Another example of a
redundant packet can be at least one of the N-protected transport
layer packets that can be recovered from the corresponding coded
packet and the remaining N-protected transport layer packets: for
example, if N=2, then only one of the first or second protected
transport layer packets used to generate the 2:1 coded packet can
be marked as discard-eligible in order to enable recovery of the
discarded packet by the receiving transport layer 14 (e.g., in the
destination host device 10').
[0092] The transport layer 14 in operation 138 stores in the
transport layer transmit buffer circuit 36 the discard-ineligible
coded packet for transfer to a deterministic network interface
circuit 22 by the device interface circuit 52 (in response to a
received "more" message 100) before any one of the N-protected
packets associated with the coded packet. Hence, the receiving
transport layer 14 can recover any discarded N-protected packet
based on the coded packet and the remaining N-protected
packets.
[0093] FIG. 7 illustrates an example diagram of the transport layer
14 in a host device (e.g., 10 or 10'') and a deterministic network
interface circuit 22 executing mitigation against a missed
transmission opportunity. The operations of FIG. 7 are for a single
deterministic network interface circuit 22; hence, the operations
of FIG. 7 are repeated for each deterministic network interface
circuit 22 allocated to the transport layer 14 for an identified
flow.
[0094] As described below, the transport layer 14 can determine a
cause of failure in a missed transmission opportunity in a
deterministic network interface circuit 22 based on updating in
operation 140 a number of packets sent (NPS) counter 142 for each
patent transfer (e.g., 144a, 144b, 144c, 144d of FIG. 7) executed
by the device interface circuit 52 in response to a "more" message
100, and based on comparing changes, between successively-received
"more" messages (e.g., 100a and 100b; 100b and 100c; and 100c and
100e) in the NPS counter 142 to changes in a successful packet
transmission (SPT) counter value 146 and a missed transmission
opportunity (MTO) counter value 148 maintained by the deterministic
network interface circuit 22.
[0095] In particular, each deterministic network interface circuit
22 tracks the total number of missed transmit opportunities (e.g.,
150a at scheduled transmission instance 84c, 150b at scheduled
transmission instance 84d, and 150c at scheduled transmission
instance 84e) by incrementing its MTO counter value 148 in response
to each missed transmit opportunity 150 in operation 152. As
illustrated in FIG. 7, the deterministic network interface circuit
22 (e.g., deterministic network interface circuit 22e of FIGS.
1H-1J) in operation 152 of FIG. 6A can increment its SPT counter
value 146 in response to successful transmission of a link layer
data packet 44 on its deterministic link 18 at a corresponding
scheduled transmission instance 84 (e.g., at scheduled transmission
instance 84a and scheduled transmission instance 84b); in contrast,
the deterministic network interface circuit 22 in operation 152 can
increment its MTO counter value 148 in response to each missed
transmit opportunity 150, namely the missed transmit opportunity
150a at the scheduled transmission instance 84c, the missed
transmit opportunity 150b at the scheduled transmission instance
84d, and the missed transmit opportunity 150c at the scheduled
transmission instance 84e. As illustrated in FIG. 7, the missed
transmit opportunity 150a is caused by the failed transfer 154a of
a packet (e.g., a transport layer packet 16, a coded packet, a
management packet, etc.) during the packet transfer 144b responsive
to the "more" message 100b, and the missed transmit opportunity
150b is caused by the failed transfer 154b of a packet during the
packet transfer 144c responsive to the "more" message 100c.
Further, the missed transmit opportunity 150c is caused by the
failed reception 156 of the "more" message 100d.
[0096] Hence, if in operation 158 the deterministic network
interface circuit 22 does not receive a transport layer packet 16
(or coded packet, management packet, etc.) before its next transmit
opportunity on the deterministic link 18 at the corresponding
scheduled transmission instance 84 (e.g., 84c) (more specifically,
before the beginning of its corresponding transmit queuing latency
78), the deterministic network interface circuit 22 in operation
158 can update its MTO counter value 148 (e.g., increment MTO=7 to
MTO=8), and generate and transmit on its deterministic link 18 a
discard-eligible OAM frame specifying an error message that a
transmit packet was not received before the scheduled transmission
instance 84c. The OAM frame enables the receiving transport layer
14 to process the OAM frame, perform any error handling (e.g.,
recovery using a network coded packet, reporting the error to the
network manager device 24, etc.) and discard the OAM frame to
preserve the queue size of its corresponding transport layer
transmit buffer circuit 36.
[0097] If, however, in operation 160 the deterministic network
interface circuit 22 successfully transmits a link layer data
packet 44 (containing, for example, a transport layer packet 16 or
a coded packet), for example as illustrated with respect to the
scheduled transmission instance 84a or the scheduled transmission
instance 84b, the deterministic network interface circuit 22 in
operation 160 increments its SPT counter value 146 (as described
with respect to operation 158, if transmission is unsuccessful then
the MTO counter value 148 is incremented but the SPT counter value
146 is not incremented).
[0098] Hence, in operation 162 the deterministic network interface
circuit 22 modifies operation 99 of FIG. 4B by generating each
"more" message 100 to include a corresponding "more" message
sequence counter (MSC) 164, its switch identifier (e.g., "Switch
1"), its queue identifier (e.g., "Queue 1"), its SPT counter value
146, and its MTO counter value 148. As illustrated in FIG. 7, the
"more" message 100a output by the deterministic network interface
circuit 22 specifies the parameters "Switch 1", "Queue 1", the MSC
value 164 of "10", the SPT counter value 146 of "1026", and the MTO
counter value 148 of "7". As described previously, each "more"
message 100 is output at least the pre-fetch interval 74 before the
next scheduled transmission instance 84, hence the "more" message
100a is output by the deterministic network interface circuit 22 at
least the pre-fetch interval 74 before the scheduled transmission
instance 84b.
[0099] Referring to FIG. 6B, the transport layer 14 detects in
operation 166 the "more" message 100 (e.g., 100a), and in response
can store the received SPT counter value 146 as a stored SPT
counter value 146', and store the received MTO counter value 148 as
a stored MTO counter value 148'.
[0100] The transport layer 14 in operation 166 also can determine
if there are any causes in failure of any missed transmit
opportunity 150 based on determining the following. The transport
layer 14 in operation 166 can determine a first difference (dNPS)
168 between a number of packet transfers 144 sent toward the
corresponding deterministic network interface circuit 22 relative
to the received "more" message 100 (e.g., 100a) and a prior request
message (not shown in FIG. 7) contiguously received from the
deterministic network interface circuit 22, illustrated in FIG. 7
as the difference (dNPS=1) 168 between the NPS counter value "1970"
142 at the receipt of the "more" message 100a, and the NPS counter
value "1969" at the receipt of the prior "more" message 100 from
the corresponding deterministic network interface circuit 22;
similarly, at reception of the "more" message 100b the difference
168 is determined as the difference between the NPS counter value
"1971" 142 at the receipt of the "more" message 100b, and the NPS
counter value "1970" at the receipt of the "more" message 100a,
hence at reception of the "more" message 100b the value is
"dNPS=1". In other words, the dNPS value "dNPS=1" 168 indicates a
successful dequeuing of a data packet from the source host device
10 toward the deterministic network interface circuit 22 via the
data link 56.
[0101] The transport layer 14 in operation 166 also can determine a
second difference (dSPT) 170 in successful packet transmissions by
the deterministic network interface circuit 22 relative to the
"more" message 100a and the prior request message 100, based on
comparing the associated SPT counter values 146. Hence, the dSPT
value "dSPT=1" 170 indicates a successful packet transmission on
the corresponding deterministic link 18 from the prior packet
transfer 144 responsive to the prior "more" message 100.
[0102] The transport layer 14 in operation 166 also can determine a
number of packet losses (NPL) 172 based on comparing the first
difference value (dNPS) 168 to the second difference value (dSPT)
170 (i.e., NPL=dNPS-dSPT) to identify any failures in transmission
on any scheduled transmission instance 84 since the last received
"more" message 100. As illustrated in FIG. 7, the NPL value 172
remains at a zero value until the failed transfer 154a of the
packet transfer 144b, which causes the deterministic network
interface circuit 22 in operation 158 to increment its MTO counter
value 148 due to the missed transmit opportunity 150a at the
scheduled transmission instance 84c, and to output in the "more"
message 100c the MTO counter value "MTO=8" 148.
[0103] Hence, the transport layer 14 responds to the "more" message
100c by determining the dSPT value 170 is equal to zero ("dSPT=0")
indicating zero transmissions since the prior "more" message 100b,
and determining the NPL value 172 is equal to one ("NPL=1"). Hence,
the NPL value 172 of "NPL=1" indicates that one failure in
transmission occurred on a scheduled transmission instance 84
between the reception of the "more" message 100c and the prior
reception of the "more" message 100b.
[0104] The transport layer 14 in operation 166 also can determine a
third difference (dMTO) 174 between the first number of any missed
transmission opportunities (e.g., MTO=8) 148 specified in the
request message (e.g., 100c) and a corresponding first number of
any missed transmission opportunities (e.g., MTO=7) 148 specified
in the previously-received request message (e.g., 100b). Since a
packet loss due to a failed transfer 154 implies a missed
opportunity, there cannot be more packet losses (quantified by the
NPL value 172) than missed opportunities (quantified by the dMTO
value 174), hence the dMTO value 174 will be greater than or equal
to the NPL value 172 (dMTO >NPL).
[0105] Hence, the transport layer 14 in operation 166 can identify
a number of lost request messages (dQ) 176, between the request
message (e.g., 100c) and the prior request message (e.g., 100b),
based on comparing the third difference (dMTO) 174 to the number of
packet losses (NPL) 172 (i.e., dQ=dMTO-NPL). As illustrated in FIG.
7, the dQ value 176 represents the number of missed opportunities
that are not due to a packet loss in a failed transfer 154 or not
due to a late arrival of a packet transfer 144 after initiation of
the transmit queuing latency 78 for the corresponding scheduled
transmission instance 84, i.e., the dQ value 176 is the sub-count
(subset) of the dMTO value 174 that is due to the failed reception
of the "more" message 100.
[0106] Hence, the transport layer 14 in operation 166 determines in
response to receiving the "more" message 100c the nonzero dMTO
value 174 value, and that the dQ value 176 is equal to zero. The
transport layer 14 in operation 178 can determine from the nonzero
dMTO value 174 and the zero dQ value 176 that the cause of failure
for the missed transmission opportunity (based on the MTO counter
value 148) is due to the failed transfer 154a of a transport layer
packet 16 (coded packet, etc.) in the packet transfer 144b from the
source host device 10 to the deterministic network interface
circuit 22, where the packet transfer 144b was not completed before
initiation of the transmit queuing latency 78 for the corresponding
scheduled transmission instance 84c. As described previously, the
failure to complete the packet transfer 144b could either be due to
a complete packet loss of the data packet on the data link 56, or
due to a "late" transfer where the packet transfer 144b was not
completed until after initiation of the transmit queuing latency 78
for the corresponding scheduled transmission instance 84c (a "late"
transfer has the same effect as the complete loss of the data
packet on the data link 56 because the "late" data packet cannot be
transmitted at the scheduled transmission instance 84c and is
therefore discarded by the deterministic network interface circuit
22).
[0107] As illustrated in operation 178 of FIG. 6B, the transport
layer 14 need not take any action because the cause of failure for
the missed transmission opportunity (as specified in the "more"
message 100c) was due to the failed transfer 154a, hence the packet
was "de-queued" (i.e., output) by the device interface circuit 52
from the source host device 10 and the packet was removed from the
transport layer transmit buffer circuit 36 accordingly, freeing up
the available storage space for the next transport layer packets 16
in the identified flow of application data.
[0108] As described previously, the ASIC 130 of the device
interface circuit 52 in operation 180 can prefetch a number of
transport layer packets 16 (e.g., two or more) from the transport
layer transmit buffer circuit 36 and store the fetched transport
layer packets 16 in the transmit buffer circuit 132. Hence, the
device interface circuit 52 can provide ASIC-class responsiveness
in providing a minimal retrieval latency 76 for responding to a
received "more" message 100 by outputting (during the next packet
transfer 144) the "next" packet queued for transmission in the
transmit buffer circuit 132. Hence, in response to the device
interface circuit 52 receiving the "more" message 100c, the ASIC
130 can notify the transport layer 14 of the received "more"
message 100 (causing the transport layer 14 to execute operations
166 and 178), and determine before transmission if a discard signal
(e.g., a 2-bit or more control signal) corresponding to the dQ
value 176 is asserted by the transport layer 14.
[0109] Since the dQ value 176 value is zero in response to the
"more" message 100c as described previously, the discard signal is
not asserted and the ASIC 130 of the device interface circuit 52 in
operation 182 can initiate the packet transfer 144 (within the
retrieval latency 76 and before initiation of the transmit queuing
latency 78 for the scheduled transmission instance 84d) of the next
packet queued for transmission in the transmit buffer circuit 132.
As illustrated in FIG. 7, the next packet that is dequeued during
the packet transfer 144c includes the corresponding MSC value 164
(MSC=12), enabling the deterministic network interface circuit 22
to associate a received packet with the previously-transmitted
"more" message 100c.
[0110] As illustrated in FIG. 7, the failed transfer 154b by the
transmit queuing latency 78 preceding the scheduled transmission
instance 84d causes the missed transmit opportunity 150b at the
scheduled transmission instance 84d; hence, the deterministic
network interface circuit 22 responds to the missed transmit
opportunity 150b by incrementing its MTO counter value 148 to
"MTO=9" in operation 152, and incrementing the sequence counter for
the MSC value 164, resulting in the deterministic network interface
circuit 22 outputting in operation 162 the "more" message 100d
specifying the MSC value 164 of "MSC=13", the SPT counter value 146
of "SPT=1027", and the MTO counter value 148 of "MTO=9". (The
deterministic network interface circuit 22 also can execute
operation 158 for transmission at the scheduled transmission
instance 84d of an OAM frame on the deterministic link 18).
However, the failed reception 156 of the "more" message 100d
results in no packet transmission by the source host device 10,
resulting in an increase in latency in the transport layer transmit
buffer circuit 36 due to the failure to dequeue the next transport
layer packet 16 from the transport layer transmit buffer circuit 36
(or the transmit buffer circuit 132) for the next scheduled
transmission instance 84e.
[0111] Consequently, the failed reception 156 of the "more" message
100d also results in the missed transmit opportunity 150c at the
scheduled transmission instance 84e, causing the deterministic
network interface circuit 22 to increment is MTO counter value 148
in operation 152, and output the "more" message 100e specifying the
MSC value 164 of "MSC=14", the SPT counter value 146 of "SPT=1027",
and the MTO counter value 148 of "MTO=10". The transport layer 14,
in response to detecting the "more" message 100e, can calculate in
operation 166 the dNPS value 168, the dSPT value 170, the NPL value
172, the dMTO value 174, and dQ value 176.
[0112] As illustrated in FIG. 7, the transport layer 14 at event
178 determines from the received "more" message 100e that the dQ
value 176 has a nonzero value ("dQ=1"), and in response the
transport layer 14 in operation 178 can assert a discard signal
asserting that "dQ=1" discard-eligible packets need to be
discarded.
[0113] The ASIC 130 in the device interface circuit 52 in operation
178 can increment an internal counter (C(DE)) according to the dQ
value 176. Since the ASIC 130 can execute more efficiently than the
transport layer operations executed by the processor circuit 12,
the ASIC 130 in the device interface circuit 52 can discard in
operation 182 the next "dQ=1" discard-eligible packets stored in
the transmit buffer circuit 132, enabling the device interface
circuit 52 in operation 182 to initiate packet transfer 144d for
the next packet stored in the transmit buffer circuit 132
(following the "dQ=1" discarded packet). Hence, the discard signal
enables the device interface circuit 52 to transfer during the
packet transfer 144d a second transport layer packet, having been
retrieved from the transport layer transmit buffer circuit 36
following the one discard-eligible transport layer packet, in
response to the "more" message 100e and prior to the transmit
queuing latency 78 of the next transmission instance 84.
[0114] As described previously, the device interface circuit 52
outputs the next packet stored in the transmit buffer circuit 132
with the sequence identifier value "MSC=14" 164 specified in the
"more" message 100e, enabling the deterministic network interface
circuit 22 identify the packet transfer 144d as responsive to the
"more" message 100e.
[0115] According to the example embodiments, the transport layer 14
can execute corrective actions, as needed for mitigation of
transmission failures and to prevent an increase in latency of the
transport layer packets 16 stored in the transport layer transmit
buffer circuit 36. Hence, the example embodiments enable a
fault-tolerant deterministic transport system that ensures that a
failed transmission opportunity does not disrupt the deterministic
transport of the transport layer packets 16 across the
deterministic links 18.
[0116] Another example of corrective action can include the
transport layer 14 in operation 184 selectively reducing the coding
ratio (N:1), for the coded packets, in response to determining a
failure in one of the deterministic network interface circuits 22.
For example, the transport layer 14 can initially set the coding
ratio to "N=4" in response to receiving from the network manager
device 24 a notification that four separate and distinct
deterministic network interface circuits 22 are allocated within
four separate and distinct switching devices 38 for the
deterministic transport of the transport layer packets 16 across
the four deterministic network interface circuits 22 in the
respective switching devices 38. The transport layer 14 can track
the continued availability of the switching devices 38 via the
"more" message 100s and/or keep-alive messages transmitted by the
switching devices 38.
[0117] In response to determining a failure in one of the
deterministic network interface circuits 22 (and or the associated
switching device 38), for example due to a failure in detecting any
keep-alive messages or "more" message 100s for a prescribed
interval, the transport layer 14 in operation 184 can reduce the
coding rate by reducing the corresponding number (N=N-1) of
allocated deterministic network interface circuits 22, changing in
this above example from "N=4" to "N=3" to provide a 3:1 rate
instead of the prior 4:1 coding rate. Hence, the lower 3:1 coding
rate can provide a lower throughput requirement across the
remaining available three deterministic network interface circuits
22, ensuring the deterministic transport across the remaining three
(3) deterministic links 18 can be maintained.
[0118] According to example embodiments, a transport layer can
mitigate against missed transmission opportunities to avoid an
increase in latency in the transport packets that need to be
deterministically transmitted across multiple deterministic links.
The discarding of discard-eligible packets can be resolved by a
receiving transport layer recovering a lost data packet using error
recovery techniques such as network coding, where a lost packet can
be recovered from an N:1 coded packet and other protected packets
used to generate the N:1 coded packet.
LATENCY CORRECTION BETWEEN TRANSPORT LAYER HOST AND DETERMINISTIC
INTERFACE CIRCUIT
[0119] FIG. 8 illustrates another example of the deterministic
interface circuits (e.g., 22e and 22f with the respective switches
"Switch 1" 38 and "Switch 3") providing deterministic transport of
transport layer packets (and/or coded packets, etc.) 16 across
multiple deterministic links 18, based on correcting latency in
retrieving transport layer packets 16 from a host device 10 or 10''
via a non-deterministic switch 181, according to an example
embodiment. As described previously (e.g., with respect to FIGS.
1H-J, 2, 6A-6B, 7), each deterministic network interface circuit 22
could be coupled to the source host device 10 via a TOR switch
device 28 providing a high-speed, low-latency data link 56 that
enables the deterministic network interface circuit 22 to send a
"more" message 100 and receive a corresponding packet transfer 144
before the next scheduled transmission instance 84.
[0120] Use of a non-deterministic switch 181, for example a
lower-cost unmanaged switch providing non-deterministic data links
56' with variable end-to-end jitter, latency, and limited
throughput between the source host device 10 and each deterministic
network interface circuit 22 can result in an inability for a
deterministic network interface circuit 22 to transmit a "more"
message 100 and receive the corresponding packet transfer 144
before the next scheduled transmission instance 84. Further, each
switching device 38 (or its corresponding deterministic network
interface circuit 22) can be connected to a different switch port
of the non-deterministic network switch 181, which may cause each
deterministic network interface circuit 22 to encounter different
latency, jitter, etc., depending on the configuration and/or status
of the non-deterministic network switch 181.
[0121] According to example embodiments, each deterministic network
interface circuit 22 can determine a round-trip latency (L) (188 of
FIG. 10) between sending a request for data to the source host
device 10 (e.g., a "more" message 100) via a non-deterministic data
link 56' (and via the non-deterministic network switch 181), and
receiving a transport layer packet 16 within a packet transfer 144
responsive to the request. Each deterministic network interface
circuit 22 can respond to the determined round-trip latency (L) 188
by sending to the source host device 10 an instruction for
initiating the packet transfer 144, where the instruction corrects
for the round-trip latency 188 and enables the deterministic
network interface circuit 22 to receive the transport layer packet
16 for transmission at the corresponding scheduled transmission
instance 84 on the corresponding deterministic link 18.
[0122] FIGS. 9A and 9B illustrate a deterministic interface circuit
correcting latency in retrieving transport layer packets from a
host device for deterministic transport on a deterministic link,
according to an example embodiment. Each deterministic network
interface circuit 22 (e.g., 22e and 22f of FIG. 8) comprises a ASIC
42, also described herein as a deterministic processing circuit
implemented as an ASIC; in other words, an ASIC implemented in the
deterministic network interface circuit 22 can execute as a
deterministic processing circuit that executes the operations
described herein, including the above-described operations of the
ASIC 42. Hence, the transmit/receive gate circuit 42 also is
referred to herein as an "ASIC" 42. In an alternate embodiment, the
deterministic processing circuit can be executed by a first ASIC in
the deterministic network interface circuit 22 and the
transmit/receive gate circuit can be executed by a different and
distinct ASIC in the deterministic network interface circuit 22.
The transmit/receive buffer circuit 40 can be implemented within a
separate and distinct memory circuit (54 of FIG. 3), and/or the
transmit/receive buffer circuit 40 can be implemented in any one of
the ASICs described herein.
[0123] The deterministic network interface circuit 22 (e.g., 22e)
can include a deterministic link transceiver 183, under the control
of the ASIC 42: the ASIC 42 is configured for establishing in
operation 200 a deterministic link 18 with its peer deterministic
network interface circuit 22 (e.g., 22i of FIGS. 1H-1J and FIG. 2)
within the deterministic data network 20, as described previously.
As described previously, the ASIC 42 establishes the deterministic
link 18 (via the deterministic link transceiver 183) per a
repeating deterministic schedule 185, where a transmission instance
84 coincides with the reception instance of the peer deterministic
network interface circuit 22, and where each scheduled transmission
instance 84 is repeated after every time interval (e.g., a "tick"
interval "TICK_INT") 186 established by the network manager device
24; in other words, the deterministic schedule 185 is maintained by
the prescribed "tick" interval 186 between each scheduled
transmission instance 84, where the deterministic network interface
circuit 22 can transmit a maximum number of "N" packets of size "F"
within a transmission time "T" that is within the "tick" interval
186. The deterministic network interface circuit 22 also includes a
non-deterministic link transceiver 187 configured for sending
"more" messages 100, and receiving packet transfers 144, via the
non-deterministic data link 56'.
[0124] FIG. 10 illustrates an example transfer window 194 that
corrects for a round-trip latency 188 by requesting a transport
layer packet at a request instance (e.g., 190a) preceding a
corresponding transmission instance (e.g., 84j) by at least the
transfer window 194, while minimizing latency in the deterministic
network interface circuit 22e, according to an example
embodiment.
[0125] The ASIC 42 in operation 202 in the deterministic network
interface circuit 22e (e.g., "Switch 1, Line Card 1" (SW1-LC1) can
determine in operation 202 a round-trip latency ("L_SW1_LC1_H") 188
between the deterministic network interface circuit 22e sending a
"more" message 100f to the source host device 10 via the
non-deterministic network switch 181 at a request instance "RO"
190a, and the deterministic network interface circuit 22e receiving
the transport layer packet 16 via a corresponding packet transfer
144 (identified by the corresponding MSC value 164 (e.g., MSC=12'')
at a corresponding reception instance "Rx0" 192a. In other words,
the round-trip latency "L_SW1_LC1_H" 188 is equal to the reception
instance "Rx0" 192a minus the request instance "R0". The round-trip
latency 188 can be recalculated, aggregated, etc., as statistically
desirable by the ASIC 42 as additional packet transfers 144 are
received.
[0126] The ASIC 42 of the deterministic network interface circuit
22e can determine in operation 204 that the round-trip latency 188
exceeds the prescribed "tick" interval 186, and in response the
ASIC 42 can set a transfer window (TW) 194 to a first integer
multiple (i=4) of the prescribed "tick" interval 186 (i.e.,
TW=i*TICK_INT), resulting in an initial transfer window (W0) having
duration equal to a first integer multiple (i=4) of the "tick"
intervals 186 (e.g., 22 milliseconds) and that exceeds the
round-trip latency 188 (i.e., TW=W0=i*TICK_INT=4*TICK_INT). As
illustrated in FIG. 10, the transport layer 14 having the initial
integer multiple of "4" "tick" intervals 186 (e.g., TW=88
milliseconds) exceeds the round-trip latency 188 (e.g., 64
milliseconds) and enables the deterministic network interface
circuit 22e to receive the packet transfer 144 at least one "tick"
interval 186 before the corresponding scheduled transmission
instance 84i allocated for the transport layer packet 16 requested
by the "more" message 100f.
[0127] The ASIC 42 of the deterministic network interface circuit
22e in operation 206 also can set a guard window (GW) to account
for any jitter variations that may be encountered in the
non-deterministic data link 56' via the non-deterministic network
switch 181, for example due to imprecise timing between the source
host device 10, the non-deterministic network switch 181, and the
deterministic network interface circuit 22e. An example value for
the guard window can be one fourth of the "tick" interval 186
(e.g., 10.5 milliseconds).
[0128] Hence, the ASIC 42 of the deterministic network interface
circuit 22e in operation 208 sends the "more" message 100f
(specifying the MSC value "12" 164) at the request instance "R0"
190a that precedes the scheduled transmission instance "TX0" 84j by
at least the transfer window (TW) 194. The ASIC 42 of the
deterministic network interface circuit 22e in operation 210 also
transmits each remaining request 100g (specifying the MSC value
"13" 164), 100h (specifying the MSC value "14" 164), and 100i
(specifying the MSC value "15" 164) of the integer multiple (i=4),
at the corresponding request instance "R1" 190b, "R2" 190c, and
"R3" 190d following the next successive "tick" interval 186, and
before expiration of the transfer window (TW) 194. Hence, the ASIC
42 of the deterministic network interface circuit 22e can transmit
multiple successive "more" messages 100g, 100h, and 100i while
awaiting the initial "more" message 100f. As described previously,
each packet transfer 144 can specify the corresponding MSC value
164, enabling the ASIC 42 of the deterministic network interface
circuit 22 to determine in operation 212 that the received packet
transfer 144f (specifying "MSC=12") for the transport layer packet
16 is responsive to the "more" message 100f (specifying
"MSC=12").
[0129] The ASIC 42 of the deterministic network interface circuit
22e in operation 212 can determine the reception instance (e.g.,
Rx0) 192a for the packet transfer 144f responsive to the "more"
message 100f, and determine whether the reception instance (e.g.,
Rx0) 192a for the packet transfer 144f was received at an excess
latency, where the value for the reception instance (e.g., Rx0)
192a is greater than the request instance "R0" 190a plus the
transfer window (TW) 194 plus the guard window.
[0130] If in operation 212 the ASIC 42 of the deterministic network
interface circuit 22 in the switching device 38 determines the
reception instance (e.g., Rx0) 192a for the transport layer packet
16 exceeded the deterministic schedule 185 and guard window (i.e.,
Rx0 >R0+TW+GW), the ASIC 42 of the deterministic network
interface circuit 22e in operation 214 can send an "exceptional"
"more" message 100 before transmission of the next scheduled "more"
message 100 at the next scheduled request instance 190. In effect,
the "exceptional" "more" message 100 serves to "jump start" the
source host device 10 into sending an extra transport layer packet
16 to avoid buffer underflow in the transmit/receive buffer circuit
40 which would cause a missed transmit opportunity. The ASIC 42 of
the deterministic network interface circuit 22e in operation 216
also can increase the size of the transfer window (TW) 194 by at
least one additional integer multiple (i=i+1) of the "tick"
interval 186; the ASIC 42 also can substantially increase the size
of the transfer window (TW) 194 by doubling the window size
(TW=2*TW) in order to aggressively capture more transport layer
packets 16 to avoid a missed transmit opportunity.
[0131] As illustrated in FIG. 9B, the deterministic network
interface circuit 22e can adjust the size of the transfer window
(TW) 194 over time to minimize the transmit buffer latency in the
transmit/receive buffer circuit 40. According to one embodiment, a
preferred transmit buffer can be reduced to the transmit/receive
buffer circuit 40 storing only a single link layer data packet 44
after each scheduled transmission instance 84, where optimally the
transmit/receive buffer circuit 40 need store a minimum of one (and
a maximum of two) packets awaiting transmission at the next
scheduled transmission instance 84.
[0132] Hence, the generation and adjustment of the transfer window
(TW) 194 in response to determining the round-trip latency 188, and
based on successive comparisons of whether the corresponding
reception instance 192 is within the transfer window (TW) 194 (and
guard window (GW)), enables the ASIC 42 of the deterministic
network interface circuit 22 to correct for latency caused by the
non-deterministic network switch 181, while minimizing queuing
latency in the transmit/receive buffer circuit 40. As described
previously with respect to FIGS. 6A, 6B, and 7, the transport layer
14 was described as determining whether a "more" message 100 was
lost based on determining the dQ value 176. According to an example
embodiment, the ASIC 42 in the deterministic network interface
circuit 22e can execute similar operations based on identifying
each "more" message 100 associated with a modulo counter value "i",
such that the source host device 10 and the deterministic network
interface circuit 22e can track the counter values, illustrated in
FIG. 7, on a per-flow basis; in other words, the counters 142, 146,
148, 168, 170, 172, 174, and 176 are reproduced for each "more"
message 100f sent at the request instance 190a for flow "R0", the
"more" message 100g sent at the request instance 190b for flow
"R1", the "more" message 100h sent at the request instance 190c for
flow "R2", and the "more" message 100i sent at the request instance
190d for the flow "R4". The counter values 142, 146, 148, 168, 170,
172, 174, and 176 can be updated for each repeating instance of the
transfer window (TW) 194. Hence, the ASIC 42 can maintain the
transport layer 146 and the transport layer 148 for each flow "j"
(e.g., for "R0", "R1", "R2", "R3") (where "j=0 to (i-1)").
[0133] Further, the deterministic network interface circuit 220 in
operation 220 can be configured for executing the operations
described above with respect to FIGS. 6A, 6B, and 7, based on
receiving from the source host device 10, for each "j" flow (e.g.,
"R0", "R1", "R2", "R3") (where "j=0 to (i-1)") the corresponding
NPS counter value 142 (e.g., NPS_R0, NPS_R1, NPS_R2, and/or NPS_R3,
referred to generally as "NPS_Rj"). In response to receiving the
NPS counter value 142 for a given flow "j", the ASIC 42 of the
deterministic network interface circuit 22e in operation 220 can
determine the associated counter values, for each flow "j",
including the dNPS value 168, dSPT value 170, NPL value 172, dMTO
value 174, and dQ value 176.
[0134] Hence, in response to detecting a dQ value 176 having a
value of "1" for a given flow "j" (i.e., dQj=1''), the ASIC 42 of
the deterministic network interface circuit 22e in operation 222
can send a discard request to the source host device 10, causing
the device interface circuit 52 to discard its next available
packet for the corresponding flow "j" from its transmit buffer
circuit 132, as described previously.
[0135] In another embodiment, the ASIC 42 of each deterministic
network interface circuit 22 can send to the source host device 10
in operation 224 an instruction in the form of a "rate-based more
message" 100 that explicitly describes a transfer rate for the host
device 10 to transfer the transport layer packets 16 at a transfer
rate based on the deterministic schedule 185 that establishes
transmission rate as the prescribed "tick" interval 186 between
each transmission instance 84. Hence, the ASIC 42 can specify a
single "rate-based more message" 100 that explicitly identifies the
"tick" interval 186 (i.e., "Transfer Rate =TICK_INT"; "Send Another
Packet After Every TICK_INT"). The device interface circuit 52 in
the source host device 10 can respond to the "rate-based more
message" 100 by immediately initiating its next packet transfer
144, and executing the next packet transfer 144 after every "tick"
interval 186 as counted by the device interface circuit 52.
[0136] As described previously, each deterministic network
interface circuit 22 communicates with the device interface circuit
52 of the source host device 10 via a non-deterministic data link
56' provided by the non-deterministic network switch 181; hence,
the clock signals maintained by the device interface circuit 52 in
the source host device 10 will not be fully synchronized in
frequency and phase with the precise clock signals maintained by
the deterministic network interface circuit 22 in accordance with
the deterministic data network 20 (e.g., according to TSN).
[0137] According to an example embodiment, the ASIC 42 can
determine latency between the deterministic network interface
circuit 22e and the source host device 10 (via the
non-deterministic network switch 181 and associated
non-deterministic data links 56) based on identifying in operation
226 a rate difference between a rate of receiving the transport
layer packets from the host device 10 (e.g., R_Rx=Rj-R(j-1)) and
the transmission rate of the deterministic schedule 185 at every
"tick" interval 186.
[0138] In response to detecting the rate of receiving (R_Rx) is
faster than the "tick" interval 186 (i.e., R_Rx <TICK_INT), the
ASIC 42 of the deterministic network interface circuit 22e in
operation 228 can send in operation 228 a timing delay message for
compensation of the rate difference by a specified delay interval,
where the timing delay message can cause the host device 10 to
delay its clock timing for the next scheduled transport layer
packet that is scheduled according to the transfer rate,
effectively "pushing back" its clock value by the specified delay
interval. The ASIC 42 of the deterministic network interface
circuit 22e in operation 228 also can output a "less" message that
operates as a suppress message for compensation of the rate
difference, causing the device interface circuit 52 in the source
host device 10 to suppress transmission of the next scheduled
transport layer packet that is scheduled according to the transfer
rate.
[0139] In response to the ASIC 42 of the deterministic network
interface circuit 22e detecting the rate of receiving (R_Rx) is
slower than the "tick" interval 186 (i.e., R_Rx >TICK_INT), the
ASIC 42 of the deterministic network interface circuit 22e in
operation 230 can send in operation 230 timing advance message that
causes the device interface circuit 52 in the source host device 10
to advance its clock timing, by a specified advance interval, for
the next scheduled transport layer packet that is scheduled
according to the transfer rate, effectively "pushing forward" its
clock value by the specified advance interval. The ASIC 42 of the
deterministic network interface circuit 22e in operation 230 also
can output an exceptional "more" message 100, as described
previously, for the next transport layer packet before the next
scheduled transport layer packet according to the transfer rate.
Hence, the device interface circuit 52 can respond to the
exceptional "more" message 100 by immediately starting the next
packet transfer 144, before expiration of the "tick" interval 186,
as an extra transmission that precedes the scheduled transfer at
the next packet transfer 144.
[0140] According to example embodiments, deterministic transport
can be established across multiple deterministic data links, even
if lower-performance switching devices are deployed between a host
device and a deterministic device interface circuit, based on
correcting for detected latencies between the transport layer host
and the deterministic interface circuit. It should be noted that
each transmission instance and associated time interval
therebetween (e.g., the "tick" interval) need not necessarily be
implemented as periodic (i.e., repeating according to a fixed
period), rather the example embodiments can be implemented using
non-periodic transmission instances where each "more" message is
transmitted to the host device circuit early enough to correct for
the latency.
[0141] While the example embodiments in the present disclosure have
been described in connection with what is presently considered to
be the best mode for carrying out the subject matter specified in
the appended claims, it is to be understood that the example
embodiments are only illustrative, and are not to restrict the
subject matter specified in the appended claims.
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